Re: [PATCH 1/3] drm: rockchip: hdmi: remove vop_crtc_mode_fixup to fix clock handling【请注意，邮件由linux-rockchip-bounces+andy.yan=rock-chips.com at lists.infradead.org代发】
Doug Anderson
dianders at chromium.org
Tue Sep 22 15:26:17 UTC 2020
Hi,
On Tue, Sep 22, 2020 at 7:52 AM Vicente Bergas <vicencb at gmail.com> wrote:
>
> On Tue, Sep 22, 2020 at 4:28 PM Doug Anderson <dianders at chromium.org> wrote:
> >
> > Hi,
> >
> > On Tue, Sep 22, 2020 at 3:13 AM crj <algea.cao at rock-chips.com> wrote:
> > >
> > > Hi, Douglas
> > >
> > > 在 2020/9/22 17:31, Vicente Bergas 写道:
> > > > On Tue, Sep 22, 2020 at 11:24 AM crj <algea.cao at rock-chips.com> wrote:
> > > >> Hello Vicente,
> > > >>
> > > >> 在 2020/9/22 15:40, Andy Yan 写道:
> > > >>> Add our HDMI driver owner Algea to list.
> > > >>>
> > > >>> On 9/22/20 2:18 AM, Vicente Bergas wrote:
> > > >>>> Under certain conditions vop_crtc_mode_fixup rounds the clock
> > > >>
> > > >> May I ask under what conditions that the clock of HDMI will
> > > >>
> > > >> be changed to 148501000? In general, the description of clock
> > > >>
> > > >> in EDID will not be detailed below the thousands place.
> > > > There is no clock in the EDID with 1KHz resolution, the clock is
> > > > 148500000 which has 500KHz resolution.
> > > > It is the function vop_crtc_mode_fixup that gets xxx0000 and returns xxx1000
> > >
> > > I checked the commit msg of commit 287422a95fe2 ("drm/rockchip: Round up
> > > _before_ giving to the clock framework").
> > >
> > > Round up hdmi clock is for some panels with special clocks. Are these
> > > panels clock can't be divided correctly common?
> >
> > I'm sorry, but I don't understand the question. Can you restate? I
> > think the commit message that you refer to is pretty thorough.
> > Specifically the problem is all around the fact that, internally, DRM
> > often refers to clocks in kHz. We end up with issues when converting
> > back and forth between numbers in kHz and in MHz. Since DRM always
> > rounds down when going to kHz we end up with problems.
> >
> > I'm curious how you're ending up with an error, though. How could
> > adding 999 to 148500000 and then rounding down cause you to get
> > 148501000?
>
> The name of the macro is DIV_ROUND_UP, or is clk_round_rate who should
> round down?
Here's the code:
rate = clk_round_rate(vop->dclk, adjusted_mode->clock * 1000 + 999);
adjusted_mode->clock = DIV_ROUND_UP(rate, 1000);
Input clock is in kHz and DRM always rounds down (last I checked--I
guess you could confirm if this is still true).
Imagine that you want an input clock of 999999 kHz and the PLL can
actually make this.
DRM will request a clock of 999 kHz because it always rounds down.
First:
rate = 999 * 1000 + 999 = 999999 Hz
Now we'll ask the clock framework if it can make this. It can, so
clk_round_rate() will return 999999 kHz. Note that, at least on all
Rockchip platforms I looked at in the past, clk_round_rate() and
clk_set_rate() always round down. Thus, if we _hadn't_ added the 999
here we would not have gotten back 999999 Hz.
We have to return a rate in terms of kHz. While we could round down
like DRM does, it seemed better at the time to do the rounding here.
Thus, I now rounded up. We should end up storing
(999999 + 999) / 1000 = 1000 kHz
Then, when we use it in vop_crtc_atomic_enable() we don't have to do
any more rounding.
I guess it's possible that the problem is that the function is
starting with an input where it knows that "adjusted_mode->clock" was
rounded down and it ends with it rounded up. That shouldn't cause
problems unless somehow the function is being called twice or someone
else is making assumptions about the rounding. You could,
potentially, change this to:
adjusted_mode->clock = rate / 1000;
...and then in vop_crtc_atomic_enable() you add the "999" back in, like:
clk_set_rate(vop->dclk, adjusted_mode->clock * 1000 + 999);
That would make it more consistent / stable. Does it work for you?
> > > >>>> 148500000 to 148501000 which leads to the following error:
> > > >>>> dwhdmi-rockchip ff940000.hdmi: PHY configuration failed (clock
> > > >>>> 148501000)
> > > >>>>
> > > >>>> The issue was found on RK3399 booting with u-boot. U-boot configures the
> > > >>>> display at 2560x1440 and then linux comes up with a black screen.
> > > >>>> A workaround was to un-plug and re-plug the HDMI display.
> > > >>>>
> > > >>>> Signed-off-by: Vicente Bergas <vicencb at gmail.com>
> > > >>>> Tested-by: Vicente Bergas <vicencb at gmail.com>
> > > >>>> ---
> > > >>>> drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 45 ---------------------
> > > >>>> 1 file changed, 45 deletions(-)
> > > >>>>
> > > >>>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> > > >>>> b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> > > >>>> index c80f7d9fd13f..fe80da652994 100644
> > > >>>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> > > >>>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> > > >>>> @@ -1142,50 +1142,6 @@ static void vop_crtc_disable_vblank(struct
> > > >>>> drm_crtc *crtc)
> > > >>>> spin_unlock_irqrestore(&vop->irq_lock, flags);
> > > >>>> }
> > > >>>> -static bool vop_crtc_mode_fixup(struct drm_crtc *crtc,
> > > >>>> - const struct drm_display_mode *mode,
> > > >>>> - struct drm_display_mode *adjusted_mode)
> > > >>>> -{
> > > >>>> - struct vop *vop = to_vop(crtc);
> > > >>>> - unsigned long rate;
> > > >>>> -
> > > >>>> - /*
> > > >>>> - * Clock craziness.
> > > >>>> - *
> > > >>>> - * Key points:
> > > >>>> - *
> > > >>>> - * - DRM works in in kHz.
> > > >>>> - * - Clock framework works in Hz.
> > > >>>> - * - Rockchip's clock driver picks the clock rate that is the
> > > >>>> - * same _OR LOWER_ than the one requested.
> > > >>>> - *
> > > >>>> - * Action plan:
> > > >>>> - *
> > > >>>> - * 1. When DRM gives us a mode, we should add 999 Hz to it.
> > > >>>> That way
> > > >>>> - * if the clock we need is 60000001 Hz (~60 MHz) and DRM
> > > >>>> tells us to
> > > >>>> - * make 60000 kHz then the clock framework will actually give us
> > > >>>> - * the right clock.
> > > >>>> - *
> > > >>>> - * NOTE: if the PLL (maybe through a divider) could actually
> > > >>>> make
> > > >>>> - * a clock rate 999 Hz higher instead of the one we want then
> > > >>>> this
> > > >>>> - * could be a problem. Unfortunately there's not much we can do
> > > >>>> - * since it's baked into DRM to use kHz. It shouldn't matter in
> > > >>>> - * practice since Rockchip PLLs are controlled by tables and
> > > >>>> - * even if there is a divider in the middle I wouldn't expect
> > > >>>> PLL
> > > >>>> - * rates in the table that are just a few kHz different.
> > > >>>> - *
> > > >>>> - * 2. Get the clock framework to round the rate for us to tell us
> > > >>>> - * what it will actually make.
> > > >>>> - *
> > > >>>> - * 3. Store the rounded up rate so that we don't need to worry
> > > >>>> about
> > > >>>> - * this in the actual clk_set_rate().
> > > >>>> - */
> > > >>>> - rate = clk_round_rate(vop->dclk, adjusted_mode->clock * 1000 +
> > > >>>> 999);
> > > >>>> - adjusted_mode->clock = DIV_ROUND_UP(rate, 1000);
> > > >>>> -
> > > >>>> - return true;
> > > >>>> -}
> > > >>>> -
> > > >>>> static bool vop_dsp_lut_is_enabled(struct vop *vop)
> > > >>>> {
> > > >>>> return vop_read_reg(vop, 0, &vop->data->common->dsp_lut_en);
> > > >>>> @@ -1512,7 +1468,6 @@ static void vop_crtc_atomic_flush(struct
> > > >>>> drm_crtc *crtc,
> > > >>>> }
> > > >>>> static const struct drm_crtc_helper_funcs vop_crtc_helper_funcs = {
> > > >>>> - .mode_fixup = vop_crtc_mode_fixup,
> > > >>>> .atomic_check = vop_crtc_atomic_check,
> > > >>>> .atomic_begin = vop_crtc_atomic_begin,
> > > >>>> .atomic_flush = vop_crtc_atomic_flush,
> > > >
> > >
> > >
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