[PATCH] backlight: pwm_bl: configure pwm only once per backlight toggle
Adam Ford
aford173 at gmail.com
Wed Oct 23 14:16:42 UTC 2019
On Fri, Oct 18, 2019 at 4:36 AM Michal Vokáč <michal.vokac at ysoft.com> wrote:
>
> On 17. 10. 19 19:44, Adam Ford wrote:
> > On Thu, Oct 17, 2019 at 12:13 PM Thierry Reding
> > <thierry.reding at gmail.com> wrote:
> >>
> >> On Thu, Oct 17, 2019 at 12:07:21PM -0500, Adam Ford wrote:
> >>> On Thu, Oct 17, 2019 at 10:14 AM Thierry Reding
> >>> <thierry.reding at gmail.com> wrote:
> >>>>
> >>>> On Thu, Oct 17, 2019 at 03:58:25PM +0200, Michal Vokáč wrote:
> >>>>> On 17. 10. 19 14:59, Thierry Reding wrote:
> >>>>>> On Thu, Oct 17, 2019 at 02:09:17PM +0200, Uwe Kleine-König wrote:
> >>>>>>> On Thu, Oct 17, 2019 at 01:11:31PM +0200, Thierry Reding wrote:
> >>>>>>>> On Thu, Oct 17, 2019 at 12:11:16PM +0200, Uwe Kleine-König wrote:
> >>>>>>>>> On Thu, Oct 17, 2019 at 11:48:08AM +0200, Michal Vokáč wrote:
> >>>>>>>>>> On 17. 10. 19 10:10, Uwe Kleine-König wrote:
> >>>>>>>>>>> A previous change in the pwm core (namely 01ccf903edd6 ("pwm: Let
> >>>>>>>>>>> pwm_get_state() return the last implemented state")) changed the
> >>>>>>>>>>> semantic of pwm_get_state() and disclosed an (as it seems) common
> >>>>>>>>>>> problem in lowlevel PWM drivers. By not relying on the period and duty
> >>>>>>>>>>> cycle being retrievable from a disabled PWM this type of problem is
> >>>>>>>>>>> worked around.
> >>>>>>>>>>>
> >>>>>>>>>>> Apart from this issue only calling the pwm_get_state/pwm_apply_state
> >>>>>>>>>>> combo once is also more effective.
> >>>>>>>>>>>
> >>>>>>>>>>> Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
> >>>>>>>>>>> ---
> >>>>>>>>>>> Hello,
> >>>>>>>>>>>
> >>>>>>>>>>> There are now two reports about 01ccf903edd6 breaking a backlight. As
> >>>>>>>>>>> far as I understand the problem this is a combination of the backend pwm
> >>>>>>>>>>> driver yielding surprising results and the pwm-bl driver doing things
> >>>>>>>>>>> more complicated than necessary.
> >>>>>>>>>>>
> >>>>>>>>>>> So I guess this patch works around these problems. Still it would be
> >>>>>>>>>>> interesting to find out the details in the imx driver that triggers the
> >>>>>>>>>>> problem. So Adam, can you please instrument the pwm-imx27 driver to
> >>>>>>>>>>> print *state at the beginning of pwm_imx27_apply() and the end of
> >>>>>>>>>>> pwm_imx27_get_state() and provide the results?
> >>>>>>>>>>>
> >>>>>>>>>>> Note I only compile tested this change.
> >>>>>>>>>>
> >>>>>>>>>> Hi Uwe,
> >>>>>>>>>> I was just about to respond to the "pwm_bl on i.MX6Q broken on 5.4-RC1+"
> >>>>>>>>>> thread that I have a similar problem when you submitted this patch.
> >>>>>>>>>>
> >>>>>>>>>> So here are my few cents:
> >>>>>>>>>>
> >>>>>>>>>> My setup is as follows:
> >>>>>>>>>> - imx6dl-yapp4-draco with i.MX6Solo
> >>>>>>>>>> - backlight is controlled with inverted PWM signal
> >>>>>>>>>> - max brightness level = 32, default brightness level set to 32 in DT.
> >>>>>>>>>>
> >>>>>>>>>> 1. Almost correct backlight behavior before 01ccf903edd6 ("pwm: Let
> >>>>>>>>>> pwm_get_state() return the last implemented state):
> >>>>>>>>>>
> >>>>>>>>>> - System boots to userspace and backlight is enabled all the time from
> >>>>>>>>>> power up.
> >>>>>>>>>>
> >>>>>>>>>> $ dmesg | grep state
> >>>>>>>>>> [ 1.763381] get state end: -1811360608, enabled: 0
> >>>>>>>>>
> >>>>>>>>> What is -1811360608? When I wrote "print *state" above, I thought about
> >>>>>>>>> something like:
> >>>>>>>>>
> >>>>>>>>> pr_info("%s: period: %u, duty: %u, polarity: %d, enabled: %d",
> >>>>>>>>> __func__, state->period, state->duty_cycle, state->polarity, state->enabled);
> >>>>>>>>>
> >>>>>>>>> A quick look into drivers/pwm/pwm-imx27.c shows that this is another
> >>>>>>>>> driver that yields duty_cycle = 0 when the hardware is off.
> >>>>>>>>
> >>>>>>>> It seems to me like the best recourse to fix this for now would be to
> >>>>>>>> patch up the drivers that return 0 when the hardware is off by caching
> >>>>>>>> the currently configured duty cycle.
> >>>>>>>>
> >>>>>>>> How about the patch below?
> >>>>>>>>
> >>>>>>>> Thierry
> >>>>>>>>
> >>>>>>>> --- >8 ---
> >>>>>>>> From 15a52a7f1b910804fabd74a5882befd3f9d6bb37 Mon Sep 17 00:00:00 2001
> >>>>>>>> From: Thierry Reding <thierry.reding at gmail.com>
> >>>>>>>> Date: Thu, 17 Oct 2019 12:56:00 +0200
> >>>>>>>> Subject: [PATCH] pwm: imx27: Cache duty cycle register value
> >>>>>>>>
> >>>>>>>> The hardware register containing the duty cycle value cannot be accessed
> >>>>>>>> when the PWM is disabled. This causes the ->get_state() callback to read
> >>>>>>>> back a duty cycle value of 0, which can confuse consumer drivers.
> >>>>>>>>
> >>>>>>>> Signed-off-by: Thierry Reding <thierry.reding at gmail.com>
> >>>>>>>> ---
> >>>>>>>> drivers/pwm/pwm-imx27.c | 31 ++++++++++++++++++++++++-------
> >>>>>>>> 1 file changed, 24 insertions(+), 7 deletions(-)
> >>>>>>>>
> >>>>>>>> diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c
> >>>>>>>> index ae11d8577f18..4113d5cd4c62 100644
> >>>>>>>> --- a/drivers/pwm/pwm-imx27.c
> >>>>>>>> +++ b/drivers/pwm/pwm-imx27.c
> >>>>>>>> @@ -85,6 +85,13 @@ struct pwm_imx27_chip {
> >>>>>>>> struct clk *clk_per;
> >>>>>>>> void __iomem *mmio_base;
> >>>>>>>> struct pwm_chip chip;
> >>>>>>>> +
> >>>>>>>> + /*
> >>>>>>>> + * The driver cannot read the current duty cycle from the hardware if
> >>>>>>>> + * the hardware is disabled. Cache the last programmed duty cycle
> >>>>>>>> + * value to return in that case.
> >>>>>>>> + */
> >>>>>>>> + unsigned int duty_cycle;
> >>>>>>>> };
> >>>>>>>> #define to_pwm_imx27_chip(chip) container_of(chip, struct pwm_imx27_chip, chip)
> >>>>>>>> @@ -155,14 +162,17 @@ static void pwm_imx27_get_state(struct pwm_chip *chip,
> >>>>>>>> tmp = NSEC_PER_SEC * (u64)(period + 2);
> >>>>>>>> state->period = DIV_ROUND_CLOSEST_ULL(tmp, pwm_clk);
> >>>>>>>> - /* PWMSAR can be read only if PWM is enabled */
> >>>>>>>> - if (state->enabled) {
> >>>>>>>> + /*
> >>>>>>>> + * PWMSAR can be read only if PWM is enabled. If the PWM is disabled,
> >>>>>>>> + * use the cached value.
> >>>>>>>> + */
> >>>>>>>> + if (state->enabled)
> >>>>>>>> val = readl(imx->mmio_base + MX3_PWMSAR);
> >>>>>>>> - tmp = NSEC_PER_SEC * (u64)(val);
> >>>>>>>> - state->duty_cycle = DIV_ROUND_CLOSEST_ULL(tmp, pwm_clk);
> >>>>>>>> - } else {
> >>>>>>>> - state->duty_cycle = 0;
> >>>>>>>> - }
> >>>>>>>> + else
> >>>>>>>> + val = imx->duty_cycle;
> >>>>>>>> +
> >>>>>>>> + tmp = NSEC_PER_SEC * (u64)(val);
> >>>>>>>> + state->duty_cycle = DIV_ROUND_CLOSEST_ULL(tmp, pwm_clk);
> >>>>>>>> if (!state->enabled)
> >>>>>>>> pwm_imx27_clk_disable_unprepare(chip);
> >>>>>>>> @@ -261,6 +271,13 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >>>>>>>> writel(duty_cycles, imx->mmio_base + MX3_PWMSAR);
> >>>>>>>> writel(period_cycles, imx->mmio_base + MX3_PWMPR);
> >>>>>>>> + /*
> >>>>>>>> + * Store the duty cycle for future reference in cases where
> >>>>>>>> + * the MX3_PWMSAR register can't be read (i.e. when the PWM
> >>>>>>>> + * is disabled).
> >>>>>>>> + */
> >>>>>>>> + imx->duty_cycle = duty_cycles;
> >>>>>>>> +
> >>>>>>>
> >>>>>>> I wonder if it would be more sensible to do this in the pwm core
> >>>>>>> instead. Currently there are two drivers known with this problem. I
> >>>>>>> wouldn't be surprised if there were more.
> >>>>>>
> >>>>>> I've inspected all the drivers and didn't spot any beyond cros-ec and
> >>>>>> i.MX that have this problem. There's also no good way to do this in the
> >>>>>> core, because the core doesn't know whether or not the driver is capable
> >>>>>> of returning the correct duty cycle on hardare readout. So the core
> >>>>>> would have to rely on state->duty_cycle that is passed in, but then the
> >>>>>> offending commit becomes useless because the whole point was to return
> >>>>>> the state as written to hardware (rather than the software state which
> >>>>>> was being returned before that patch).
> >>>>>>
> >>>>>>> If we want to move clients to not rely on .period and .duty_cycle for a
> >>>>>>> disabled PWM (do we?) a single change in the core is also beneficial
> >>>>>>> compared to fixing several lowlevel drivers.
> >>>>>>
> >>>>>> These are really two orthogonal problems. We don't currently consider
> >>>>>> enabled = 0 to be equivalent to duty_cycle = 0 at an API level. I'm not
> >>>>>> prepared to do that at this point in the release cycle either.
> >>>>>>
> >>>>>> What this here has shown is that we have at least two drivers that don't
> >>>>>> behave the way they are supposed to according to the API and they break
> >>>>>> consumers. If they break for pwm-backlight, it's possible that they will
> >>>>>> break for other consumers as well. So the right thing to do is fix the
> >>>>>> two drivers that are broken.
> >>>>>>
> >>>>>> After -rc1 we no longer experiment. Instead we clean up the messes we've
> >>>>>> made. We can revisit the other points once mainline is fixed.
> >>>>>
> >>>>> Hi Thierry,
> >>>>> I just tried your patch with v5.4-rc3 with this result:
> >>>>>
> >>>>> root at hydraco:~# dmesg | grep pwm_
> >>>>> [ 1.772089] pwm_imx27_get_state: period: 992970, duty: 0, polarity: 0, enabled: 0
> >>>>> [ 4.938759] pwm_imx27_apply: period: 500000, duty: 0, polarity: 1, enabled: 0
> >>>>> [ 4.947431] pwm_imx27_get_state: period: 992970, duty: 0, polarity: 0, enabled: 0
> >>>>
> >>>> Okay... this is interesting. If I understand correctly, that first line
> >>>> here is where the initial hardware readout happens. The second one is
> >>>> the first time when the backlight is configured, so it sets period and
> >>>> polarity. But then for some reason when we read out after that to read
> >>>> what state was written... we see that actually nothing was written at
> >>>> all.
> >>>>
> >>>> And we can see why in pwm_imx27_apply(): If the PWM is not enabled, we
> >>>> don't actually program any of the registers, so it's not a surprise that
> >>>> things fall apart.
> >>>>
> >>>>> [ 4.956484] pwm_imx27_apply: period: 992970, duty: 992970, polarity: 0, enabled: 0
> >>>>> [ 4.965473] pwm_imx27_get_state: period: 992970, duty: 0, polarity: 0, enabled: 0
> >>>>> [ 4.974410] pwm_imx27_apply: period: 992970, duty: 0, polarity: 0, enabled: 1
> >>>>> [ 4.988617] pwm_imx27_get_state: period: 992970, duty: 0, polarity: 0, enabled: 1
> >>>>>
> >>>>> Backlight is on with full brightness at this stage.
> >>>>>
> >>>>> root at hydraco:/sys/class/backlight/backlight# cat brightness
> >>>>> 32
> >>>>>
> >>>>> root at hydraco:/sys/class/backlight/backlight# echo 32 > brightness
> >>>>> [ 153.386391] pwm_imx27_apply: period: 992970, duty: 992970, polarity: 0, enabled: 1
> >>>>> [ 153.398311] pwm_imx27_get_state: period: 992970, duty: 992970, polarity: 0, enabled: 1
> >>>>>
> >>>>> Backlight goes down.
> >>>>>
> >>>>> root at hydraco:/sys/class/backlight/backlight# echo 1 > brightness
> >>>>> [ 168.506261] pwm_imx27_apply: period: 992970, duty: 15576, polarity: 0, enabled: 1
> >>>>> [ 168.518064] pwm_imx27_get_state: period: 992970, duty: 15576, polarity: 0, enabled: 1
> >>>>>
> >>>>> Backlight goes up to almost full brightness.
> >>>>>
> >>>>> root at hydraco:/sys/class/backlight/backlight# echo 0 > brightness
> >>>>> [ 177.496265] pwm_imx27_apply: period: 992970, duty: 0, polarity: 0, enabled: 0
> >>>>> [ 177.507602] pwm_imx27_get_state: period: 496485, duty: 7788, polarity: 0, enabled: 0
> >>>>>
> >>>>> Backlight goes up to full brightness.
> >>>>>
> >>>>> So your patch does not solve my issue.
> >>>>>
> >>>>> The main problem I see is incorrect polarity setting. In my DT
> >>>>> the pwm-backlight consumer requests PWM_POLARITY_INVERTED and
> >>>>> period 500000ns. Though after reset the PWM HW registers are
> >>>>> configured to normal polarity. This initial setting is read out
> >>>>> and used by the consumer instead of the DT configuration.
> >>>>
> >>>> So the problem with the i.MX driver is that it doesn't actually write
> >>>> the full state to the hardware and therefore the patch that caused these
> >>>> things to break reads back an incomplete state. So we've basically got
> >>>> two options: 1) make sure the hardware state is fully written or 2) make
> >>>> sure that we return the cached state.
> >>>>
> >>>> I think 2) doesn't really make sense because it is conflicts with the
> >>>> purpose of the ->get_state() callback. The only time where we should be
> >>>> returning cached data is if the hardware registers don't contain the
> >>>> information (as in the case of the cros-ec driver) or if we can't access
> >>>> it for other reasons (such as in the case of i.MX's duty cycle).
> >>>>
> >>>> Does the attached patch help with your issue? The idea is to always
> >>>> write the full state to the hardware, even if period and duty cycle are
> >>>> unused when the PWM is disabled. That's really the kind of contract that
> >>>> we have added with the offending patch in the core.
> >>>>
> >>>> It looks like all other drivers handle this more or less correctly, so
> >>>> if we only need to fix up cros-ec and i.MX this seems like a realistic
> >>>> way to fix things up. If other drivers are problematic in this regard,
> >>>> we should probably revert and then fix the drivers before we can apply
> >>>> that patch again.
> >>>
> >>> This patch combined with your previous patch appears to have worked.
> >>> If you end up sending a patch series to fix this, go ahead and add
> >>>
> >>> Tested-by: Adam Ford <aford173 at gmail.com> #imx6q-logicpd
> >>
> >> Excellent! Thanks for testing this. I'll wait until tomorrow to see if
> >> there's some feedback from Enric for the cros-ec change. I'll send out
> >> the total of three patches again in the hopes that those are really
> >> the only two cases that are broken.
> >
> > When you do, can you mark it with the Fixes note? I am hoping the
> > maintainers can hopefully incorporate this into 5.4 since it fixes a
> > regression.
>
> Hi Thierry,
>
> I can confirm that the combination of your two patches:
> - ("pwm: imx27: Unconditionally write state to hardware")
> - ("pwm: imx27: Cache duty cycle register value")
>
> works OK and solve my problem as well.
>
> root at hydraco:~# dmesg | grep pwm_
> [ 1.695306] pwm_imx27_get_state: period: 992970, duty: 0, polarity: 0, enabled: 0
> [ 5.387271] pwm_imx27_apply: period: 500000, duty: 0, polarity: 1, enabled: 0
> [ 5.396433] pwm_imx27_get_state: period: 500000, duty: 0, polarity: 1, enabled: 0
> [ 5.405500] pwm_imx27_apply: period: 500000, duty: 500000, polarity: 1, enabled: 0
> [ 5.418802] pwm_imx27_get_state: period: 500000, duty: 500000, polarity: 1, enabled: 0
> [ 5.428208] pwm_imx27_apply: period: 500000, duty: 500000, polarity: 1, enabled: 1
> [ 5.442633] pwm_imx27_get_state: period: 500000, duty: 500000, polarity: 1, enabled: 1
>
> Backlight is on from power up to userspace.
>
> root at hydraco:~# cd /sys/class/backlight/backlight/
> root at hydraco:/sys/devices/soc0/backlight/backlight/backlight# cat brightness
> 32
>
> root at hydraco:/sys/devices/soc0/backlight/backlight/backlight# echo 32 > brightness
>
> Nothing happens.
>
> root at hydraco:/sys/devices/soc0/backlight/backlight/backlight# echo 1 > brightness
> [ 513.629043] pwm_imx27_apply: period: 500000, duty: 7843, polarity: 1, enabled: 1
> [ 513.639899] pwm_imx27_get_state: period: 500000, duty: 7833, polarity: 1, enabled: 1
>
> Backlight goes to low brightness.
>
> root at hydraco:/sys/devices/soc0/backlight/backlight/backlight# echo 0 > brightness
> [ 519.677088] pwm_imx27_apply: period: 500000, duty: 0, polarity: 1, enabled: 0
> [ 519.687733] pwm_imx27_get_state: period: 500000, duty: 0, polarity: 1, enabled: 0
>
> Backlight goes to max brightness, unresolved i.MX6 limitation.
>
> root at hydraco:/sys/devices/soc0/backlight/backlight/backlight# echo 32 > brightness
> [ 923.921292] pwm_imx27_apply: period: 500000, duty: 500000, polarity: 1, enabled: 0
> [ 923.933331] pwm_imx27_get_state: period: 500000, duty: 500000, polarity: 1, enabled: 0
> [ 923.944546] pwm_imx27_apply: period: 500000, duty: 500000, polarity: 1, enabled: 1
> [ 923.963931] pwm_imx27_get_state: period: 500000, duty: 500000, polarity: 1, enabled: 1
>
> Backlight remains at max brightness, OK.
>
> If I apply the patch from Uwe ("backlight: pwm_bl: configure pwm only once
> per backlight toggle") on top of that, it still works and I do not see
> any change in the behavior.
>
> root at hydraco:~# dmesg | grep pwm_
> [ 1.687461] pwm_imx27_get_state: period: 992970, duty: 0, polarity: 0, enabled: 0
> [ 4.875087] pwm_imx27_apply: period: 500000, duty: 0, polarity: 1, enabled: 0
> [ 4.884796] pwm_imx27_get_state: period: 500000, duty: 0, polarity: 1, enabled: 0
> [ 4.893922] pwm_imx27_apply: period: 500000, duty: 500000, polarity: 1, enabled: 1
> [ 4.908473] pwm_imx27_get_state: period: 500000, duty: 500000, polarity: 1, enabled: 1
>
> root at hydraco:~# cd /sys/class/backlight/backlight/
> root at hydraco:/sys/devices/soc0/backlight/backlight/backlight# cat brightness
> 32
>
> root at hydraco:/sys/devices/soc0/backlight/backlight/backlight# echo 32 > brightness
>
> root at hydraco:/sys/devices/soc0/backlight/backlight/backlight# echo 1 > brightness
> [ 110.775650] pwm_imx27_apply: period: 500000, duty: 7843, polarity: 1, enabled: 1
> [ 110.786512] pwm_imx27_get_state: period: 500000, duty: 7833, polarity: 1, enabled: 1
>
> root at hydraco:/sys/devices/soc0/backlight/backlight/backlight# echo 0 > brightness
> [ 128.224036] pwm_imx27_apply: period: 500000, duty: 0, polarity: 1, enabled: 0
> [ 128.234675] pwm_imx27_get_state: period: 500000, duty: 0, polarity: 1, enabled: 0
>
> root at hydraco:/sys/devices/soc0/backlight/backlight/backlight# echo 32 > brightness
> [ 138.208072] pwm_imx27_apply: period: 500000, duty: 500000, polarity: 1, enabled: 1
> [ 138.220271] pwm_imx27_get_state: period: 500000, duty: 500000, polarity: 1, enabled: 1
>
> The only difference is here when the state is changed from enabled=0
> to enabled=1. The apply/get_state combo is called only once.
>
> So this looks good to me.
>
> Tested-by: Michal Vokáč <michal.vokac at ysoft.com>
>
> Thank you all for the very prompt reaction!
What is the plan to address the regression for 5.4? I wasn't sure if
we're going to apply the i.mx fixes or temporarily revert the
offending patch, or something else. (or maybe nothing at all)
thanks
adam
> Michal
>
> >>>> --- >8 ---
> >>>> From 7040f0038e04a1caa6dda5b6f675a9fdee0271f4 Mon Sep 17 00:00:00 2001
> >>>> From: Thierry Reding <thierry.reding at gmail.com>
> >>>> Date: Thu, 17 Oct 2019 17:11:41 +0200
> >>>> Subject: [PATCH] pwm: imx27: Unconditionally write state to hardware
> >>>>
> >>>> The i.MX driver currently uses a shortcut and doesn't write all of the
> >>>> state through to the hardware when the PWM is disabled. This causes an
> >>>> inconsistent state to be read back by consumers with the result of them
> >>>> malfunctioning.
> >>>>
> >>>> Fix this by always writing the full state through to the hardware
> >>>> registers so that the correct state can always be read back.
> >>>>
> >>>> Signed-off-by: Thierry Reding <thierry.reding at gmail.com>
> >>>> ---
> >>>> drivers/pwm/pwm-imx27.c | 120 ++++++++++++++++++++--------------------
> >>>> 1 file changed, 59 insertions(+), 61 deletions(-)
> >>>>
> >>>> diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c
> >>>> index 4113d5cd4c62..59d8b1289808 100644
> >>>> --- a/drivers/pwm/pwm-imx27.c
> >>>> +++ b/drivers/pwm/pwm-imx27.c
> >>>> @@ -230,70 +230,68 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >>>>
> >>>> pwm_get_state(pwm, &cstate);
> >>>>
> >>>> - if (state->enabled) {
> >>>> - c = clk_get_rate(imx->clk_per);
> >>>> - c *= state->period;
> >>>> -
> >>>> - do_div(c, 1000000000);
> >>>> - period_cycles = c;
> >>>> -
> >>>> - prescale = period_cycles / 0x10000 + 1;
> >>>> -
> >>>> - period_cycles /= prescale;
> >>>> - c = (unsigned long long)period_cycles * state->duty_cycle;
> >>>> - do_div(c, state->period);
> >>>> - duty_cycles = c;
> >>>> -
> >>>> - /*
> >>>> - * according to imx pwm RM, the real period value should be
> >>>> - * PERIOD value in PWMPR plus 2.
> >>>> - */
> >>>> - if (period_cycles > 2)
> >>>> - period_cycles -= 2;
> >>>> - else
> >>>> - period_cycles = 0;
> >>>> -
> >>>> - /*
> >>>> - * Wait for a free FIFO slot if the PWM is already enabled, and
> >>>> - * flush the FIFO if the PWM was disabled and is about to be
> >>>> - * enabled.
> >>>> - */
> >>>> - if (cstate.enabled) {
> >>>> - pwm_imx27_wait_fifo_slot(chip, pwm);
> >>>> - } else {
> >>>> - ret = pwm_imx27_clk_prepare_enable(chip);
> >>>> - if (ret)
> >>>> - return ret;
> >>>> -
> >>>> - pwm_imx27_sw_reset(chip);
> >>>> - }
> >>>> -
> >>>> - writel(duty_cycles, imx->mmio_base + MX3_PWMSAR);
> >>>> - writel(period_cycles, imx->mmio_base + MX3_PWMPR);
> >>>> -
> >>>> - /*
> >>>> - * Store the duty cycle for future reference in cases where
> >>>> - * the MX3_PWMSAR register can't be read (i.e. when the PWM
> >>>> - * is disabled).
> >>>> - */
> >>>> - imx->duty_cycle = duty_cycles;
> >>>> -
> >>>> - cr = MX3_PWMCR_PRESCALER_SET(prescale) |
> >>>> - MX3_PWMCR_STOPEN | MX3_PWMCR_DOZEN | MX3_PWMCR_WAITEN |
> >>>> - FIELD_PREP(MX3_PWMCR_CLKSRC, MX3_PWMCR_CLKSRC_IPG_HIGH) |
> >>>> - MX3_PWMCR_DBGEN | MX3_PWMCR_EN;
> >>>> -
> >>>> - if (state->polarity == PWM_POLARITY_INVERSED)
> >>>> - cr |= FIELD_PREP(MX3_PWMCR_POUTC,
> >>>> - MX3_PWMCR_POUTC_INVERTED);
> >>>> -
> >>>> - writel(cr, imx->mmio_base + MX3_PWMCR);
> >>>> - } else if (cstate.enabled) {
> >>>> - writel(0, imx->mmio_base + MX3_PWMCR);
> >>>> + c = clk_get_rate(imx->clk_per);
> >>>> + c *= state->period;
> >>>>
> >>>> - pwm_imx27_clk_disable_unprepare(chip);
> >>>> + do_div(c, 1000000000);
> >>>> + period_cycles = c;
> >>>> +
> >>>> + prescale = period_cycles / 0x10000 + 1;
> >>>> +
> >>>> + period_cycles /= prescale;
> >>>> + c = (unsigned long long)period_cycles * state->duty_cycle;
> >>>> + do_div(c, state->period);
> >>>> + duty_cycles = c;
> >>>> +
> >>>> + /*
> >>>> + * according to imx pwm RM, the real period value should be PERIOD
> >>>> + * value in PWMPR plus 2.
> >>>> + */
> >>>> + if (period_cycles > 2)
> >>>> + period_cycles -= 2;
> >>>> + else
> >>>> + period_cycles = 0;
> >>>> +
> >>>> + /*
> >>>> + * Wait for a free FIFO slot if the PWM is already enabled, and flush
> >>>> + * the FIFO if the PWM was disabled and is about to be enabled.
> >>>> + */
> >>>> + if (cstate.enabled) {
> >>>> + pwm_imx27_wait_fifo_slot(chip, pwm);
> >>>> + } else {
> >>>> + ret = pwm_imx27_clk_prepare_enable(chip);
> >>>> + if (ret)
> >>>> + return ret;
> >>>> +
> >>>> + pwm_imx27_sw_reset(chip);
> >>>> }
> >>>>
> >>>> + writel(duty_cycles, imx->mmio_base + MX3_PWMSAR);
> >>>> + writel(period_cycles, imx->mmio_base + MX3_PWMPR);
> >>>> +
> >>>> + /*
> >>>> + * Store the duty cycle for future reference in cases where the
> >>>> + * MX3_PWMSAR register can't be read (i.e. when the PWM is disabled).
> >>>> + */
> >>>> + imx->duty_cycle = duty_cycles;
> >>>> +
> >>>> + cr = MX3_PWMCR_PRESCALER_SET(prescale) |
> >>>> + MX3_PWMCR_STOPEN | MX3_PWMCR_DOZEN | MX3_PWMCR_WAITEN |
> >>>> + FIELD_PREP(MX3_PWMCR_CLKSRC, MX3_PWMCR_CLKSRC_IPG_HIGH) |
> >>>> + MX3_PWMCR_DBGEN;
> >>>> +
> >>>> + if (state->polarity == PWM_POLARITY_INVERSED)
> >>>> + cr |= FIELD_PREP(MX3_PWMCR_POUTC,
> >>>> + MX3_PWMCR_POUTC_INVERTED);
> >>>> +
> >>>> + if (state->enabled)
> >>>> + cr |= MX3_PWMCR_EN;
> >>>> +
> >>>> + writel(cr, imx->mmio_base + MX3_PWMCR);
> >>>> +
> >>>> + if (!state->enabled && cstate.enabled)
> >>>> + pwm_imx27_clk_disable_unprepare(chip);
> >>>> +
> >>>> return 0;
> >>>> }
> >>>>
> >>>> --
> >>>> 2.23.0
> >>>>
>
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