armada_drm clock selection
Russell King - ARM Linux
linux at arm.linux.org.uk
Fri Jun 28 14:18:48 PDT 2013
On Fri, Jun 28, 2013 at 04:11:32PM -0400, Daniel Drake wrote:
> Hi Russell,
>
> Thanks for pointing me to the most recent version of your driver.
> Can you comment on the below patch for improved clock handling?
Sure... lets add some background info first: the big problem here is the
completely different register layouts for the clock register:
On Armada 510:
31:30 - select the clock input from 4 possible sources:
0 - AXI, 1 - EXT0, 2 - PLL, 3 - EXT1
29 - loads the divider values
27:16 - (broken) fractional divider - you never want to use this
15:0 - integer divider
Armada 16x:
31:28 - select clock input from 4 possible sources using bit patterns.
0 - AHB, 1 - PCLK, 2 - AXI, 3 - PLL
27:16 - (broken) fractional divider
15:0 - integer divider
>From drivers/video/mmp driver (MMP2/MMP3, aka Armada 610?):
31 - clock select
28 - disable bit
27:16 - fractional divider
15:12 - apparantly not used
11:8 - DSI divider
7:0 - integer divider
So we have at least three rather different layouts of this register to
deal with different a divider range and different clock selection
methods. Hence why I separated out the functionality into a callback...
> It is based on the approach in Jean-Francois Moine's driver, and would
> serve for the basis of having clock info come from the DT. If you have
> something else in mind, maybe you can explain quickly, and I'll try to
> implement it.
Yes, I really don't like how you got rid of the initial call to the
compute function... we need to have some way to reject mode setting
for clock rates which we can't support, and that was it. Ideally,
this should be done to limit the available modes, but as DRM doesn't
ask the CRTC itself whether a particular mode is valid... that's a
shortcoming of DRM.
For example, we need to reject the TV modes if there is no clock
capable of providing something close enough to the required rate.
> armada_priv now has a clk array, the indice of each member of the array
> corresponds to the id in the SCLK register (so extclk1 goes at clk[3]).
> When we need to set up SCLK for a CRTC, we try to find a clock that can
> meet the requested rate exactly. If we don't find one, we fall back on the
> first clock in the array.
I've steered clear of doing anything like this with Armada 510 because
the documentation is too totally and utterly diabolical that it's
impossible to really work out what this "AXI" or "PLL" clock is, how
they're clocked, what rate they're clocked at, and what clock they
correspond to in the kernel.
Moreover, according to Sebastian, the internal clocks are totally and
utterly useless for HDMI resolutions - and as all I can use on my setup
are the TV resolutions...
> armada510_compute_crtc_clock had a fair amount of stuff that is in danger
> of being repeated in a MMP2-equivalent function, and then again for MMP3.
> So I took out the clock-hunting code and made that into a function that
> would be shared by the 3 platforms.
Well, the solution to that is to provide a helper for the compute
function(s) to use, not to bolt the assumptions about clocks into the
CRTC part of the driver. Eg, it appears some platforms would only have
two clock inputs.
> devm can't be used for clocks as for DT we will use of_clk_get() with
> an index and there is no devm equivalent.
devm_clk_get() should work on DT. I've been through this before with
the DT people, and they've come back and told me that it does work with
DT. You're telling me it doesn't, which means someone is either
mistaken.
My guess is you're missing a "clock names" property. Given that these
controllers seem to be able to source from many different sources
depending on the clock, I think requiring the clock names property is
reasonable because there is little consistency between what each clock
is used for.
> Comments appreciated. Compile tested only.
> ---
> drivers/gpu/drm/armada/armada_crtc.c | 31 ++++++++---
> drivers/gpu/drm/armada/armada_drm.h | 15 +++--
> drivers/gpu/drm/armada/armada_drv.c | 104 ++++++++++++++++++++---------------
> drivers/gpu/drm/armada/armada_hw.h | 9 +--
> 4 files changed, 100 insertions(+), 59 deletions(-)
>
> diff --git a/drivers/gpu/drm/armada/armada_crtc.c b/drivers/gpu/drm/armada/armada_crtc.c
> index dadaf63..9705466 100644
> --- a/drivers/gpu/drm/armada/armada_crtc.c
> +++ b/drivers/gpu/drm/armada/armada_crtc.c
> @@ -413,16 +413,31 @@ static int armada_drm_crtc_mode_set(struct drm_crtc *crtc,
> struct armada_private *priv = crtc->dev->dev_private;
> struct armada_crtc *dcrtc = drm_to_armada_crtc(crtc);
> struct armada_regs regs[16];
> + struct clk *clk;
> uint32_t lm, rm, tm, bm, val, sclk;
> unsigned long flags;
> unsigned i;
> bool interlaced;
> + int clk_idx;
> int ret;
>
> - /* First, check that this will succeed. */
> - ret = priv->ops->compute_crtc_clock(dcrtc, adj, NULL);
> - if (ret)
> - return ret;
> + /* First, check that a suitable clock is available. */
> + clk_idx = armada_drm_find_best_clock(priv, adj->clock * 1000);
> + if (clk_idx < 0)
> + return clk_idx;
> +
> + clk = priv->clk[clk_idx];
> + if (dcrtc->clk != clk) {
> + if (dcrtc->clk) {
> + clk_disable_unprepare(clk);
> + dcrtc->clk = NULL;
> + }
> +
> + ret = clk_prepare_enable(clk);
> + if (ret)
> + return ret;
> + dcrtc->clk = clk;
(a) Some clocks can only really report what rate they can give if they've
been prepared (think about non-running PLLs upstream of the clock).
(b) The assumption that NULL is not a valid clock is itself invalid
(you reverted best practice wrt that in this driver - thanks for that.)
(c) don't fall into the trap that clk_prepare_enable() replaces
clk_prepare() and clk_enable(). It doesn't. clk_prepare_enable() was
to be a transition function to the new API, not a permanent thing. Use
of the original functions is still valid.
> + }
>
> drm_framebuffer_reference(crtc->fb);
>
> @@ -459,8 +474,8 @@ static int armada_drm_crtc_mode_set(struct drm_crtc *crtc,
> writel_relaxed(val, dcrtc->base + LCD_SPU_DUMB_CTRL);
> }
>
> - /* Now compute the divider for real */
> - priv->ops->compute_crtc_clock(dcrtc, adj, &sclk);
> + /* Now compute the divider */
> + sclk = priv->ops->compute_crtc_clock(dcrtc, adj->clock * 1000, clk_idx);
That looks to me like a backwards step - not passing the full mode
information. What if there's something in there (eg, CLKBY2 flag
which DRM doesn't seem to document) which we might want to make use of?
> armada_reg_queue_set(regs, i, sclk, LCD_CFG_SCLK_DIV);
>
> @@ -634,7 +649,7 @@ static void armada_drm_crtc_destroy(struct drm_crtc *crtc)
> priv->dcrtc[dcrtc->num] = NULL;
> drm_crtc_cleanup(&dcrtc->crtc);
>
> - if (!IS_ERR(dcrtc->clk))
> + if (dcrtc->clk)
See (b) above.
> clk_disable_unprepare(dcrtc->clk);
>
> kfree(dcrtc);
> @@ -734,7 +749,7 @@ int armada_drm_crtc_create(struct drm_device *dev, unsigned num,
>
> dcrtc->base = base;
> dcrtc->num = num;
> - dcrtc->clk = ERR_PTR(-EINVAL);
> + dcrtc->clk = NULL;
See (b) above.
> dcrtc->cfg_dma_ctrl0 = CFG_GRA_ENA | CFG_GRA_HSMOOTH;
> dcrtc->cfg_dumb_ctrl = DUMB24_RGB888_0;
> spin_lock_init(&dcrtc->irq_lock);
> diff --git a/drivers/gpu/drm/armada/armada_drm.h b/drivers/gpu/drm/armada/armada_drm.h
> index c2dcde5..b41d77c 100644
> --- a/drivers/gpu/drm/armada/armada_drm.h
> +++ b/drivers/gpu/drm/armada/armada_drm.h
> @@ -41,18 +41,23 @@ struct armada_private;
>
> struct armada_ops {
> int (*init)(struct armada_private *, struct device *);
> - int (*compute_crtc_clock)(struct armada_crtc *,
> - const struct drm_display_mode *,
> - uint32_t *);
> + uint32_t (*compute_crtc_clock)(struct armada_crtc *,
> + long rate, int clk_idx);
> };
>
> +#define ARMADA_MAX_CLOCK 4
> +
> struct armada_private {
> const struct armada_ops *ops;
> struct drm_fb_helper *fbdev;
> struct armada_crtc *dcrtc[2];
> struct armada_overlay *overlay;
> struct drm_mm linear;
> - struct clk *extclk[2];
> +
> + /* The index of clocks in this array line up with their ID
> + * into the SCLK clock selection register. */
> + struct clk *clk[ARMADA_MAX_CLOCK];
> +
> #ifdef CONFIG_DEBUG_FS
> struct dentry *de;
> #endif
> @@ -70,4 +75,6 @@ void armada_drm_overlay_off(struct drm_device *, struct armada_overlay *);
> int armada_drm_debugfs_init(struct drm_minor *);
> void armada_drm_debugfs_cleanup(struct drm_minor *);
>
> +int armada_drm_find_best_clock(struct armada_private *priv, long needed_rate);
> +
> #endif
> diff --git a/drivers/gpu/drm/armada/armada_drv.c b/drivers/gpu/drm/armada/armada_drv.c
> index 807fd35..a6fc3f1 100644
> --- a/drivers/gpu/drm/armada/armada_drv.c
> +++ b/drivers/gpu/drm/armada/armada_drv.c
> @@ -16,68 +16,71 @@
> #include "armada_ioctl.h"
> #include "armada_ioctlP.h"
>
> +int armada_drm_find_best_clock(struct armada_private *priv, long needed_rate)
> +{
> + int i;
> +
> + /* check if any clock can meet this rate directly */
> + for (i = 0; i < ARMADA_MAX_CLOCK; i++) {
> + struct clk *clk = priv->clk[i];
> + long ref;
> +
> + if (!clk)
> + continue;
> +
> + clk_set_rate(clk, needed_rate);
> + ref = clk_get_rate(clk);
> +
> + if (ref % needed_rate == 0)
> + return i;
> + }
> +
> + /* fallback: return first available clock */
> + for (i = 0; i < ARMADA_MAX_CLOCK; i++) {
> + struct clk *clk = priv->clk[i];
> + if (clk)
> + return i;
> + }
> +
> + return -ENOENT;
> +}
This can be a library function called by the compute_clock implementation.
However, it's buggy. It's not returning the best clock. If we're going
to go to the expense of potentially causing the clock tree to recalculate
for every clock connected to this device, then we'd better do a good job
here.
That is - compute the source clock which can give us the _best_
approximation to the required clock. We're almost doing that with the
"ref % needed_rate" line, so if we're already doing that calculation,
let's track for each iteration whether the clock gives us a better match
than our previous one - and return the best approximation.
And why use clk_set_rate()/clk_get_rate()? (a) what if clk_set_rate()
fails (the API allows it to.) (b) what's wrong with clk_round_rate()?
> +
> /*
> * Armada510 specific initialization. There _may_ be two external
> * clocks - look them up now but don't fail if they're not present.
> * We may be able to use the internal clocks instead.
> + *
> + * We currently are pretty rudimentary here, always selecting EXT_REF_CLK_1
> */
> static int armada510_init(struct armada_private *priv, struct device *dev)
> {
> - priv->extclk[0] = devm_clk_get(dev, "ext_ref_clk_1");
> + struct clk *clk = clk_get(dev, "ext_ref_clk_1");
This is definitely a backwards step (and see above).
>
> - if (IS_ERR(priv->extclk[0])) {
> - int ret = PTR_ERR(priv->extclk[0]);
> + if (IS_ERR(clk)) {
> + int ret = PTR_ERR(clk);
> if (ret == -ENOENT)
> ret = -EPROBE_DEFER;
> return ret;
> }
>
> + priv->clk[SCLK_510_EXTCLK1] = clk;
Do you really want to use a register setting (which only has the top
two bits set) as an array index? :) We aren't 64-bit on these
platforms...
> return 0;
> }
>
> -/*
> - * Armada510 specific SCLK register selection: this gets called with
> - * sclk = NULL to test whether the mode is supportable, and again with
> - * sclk != NULL to set the clocks up for that. The former can return
> - * an error, but the latter is expected not to.
> - *
> - * We currently are pretty rudimentary here, always selecting
> - * EXT_REF_CLK_1 for LCD0 and erroring LCD1. This needs improvement!
> - */
> -static int armada510_compute_crtc_clock(struct armada_crtc *dcrtc,
> - const struct drm_display_mode *mode, uint32_t *sclk)
> +static uint32_t armada510_compute_crtc_clock(struct armada_crtc *dcrtc,
> + long rate, int clk_idx)
> {
> struct armada_private *priv = dcrtc->crtc.dev->dev_private;
> - struct clk *clk = priv->extclk[0];
> - int ret;
> + struct clk *clk = priv->clk[clk_idx];
> + uint32_t ref, div;
>
> - if (dcrtc->num == 1)
> - return -EINVAL;
> + ref = clk_round_rate(clk, rate);
> + div = DIV_ROUND_UP(ref, rate);
> + if (div < 1)
> + div = 1;
>
> - if (IS_ERR(clk))
> - return PTR_ERR(clk);
> -
> - if (dcrtc->clk != clk) {
> - ret = clk_prepare_enable(clk);
> - if (ret)
> - return ret;
> - dcrtc->clk = clk;
> - }
> -
> - if (sclk) {
> - uint32_t rate, ref, div;
> -
> - rate = mode->clock * 1000;
> - ref = clk_round_rate(clk, rate);
> - div = DIV_ROUND_UP(ref, rate);
> - if (div < 1)
> - div = 1;
> -
> - clk_set_rate(clk, ref);
> - *sclk = div | SCLK_510_EXTCLK1;
> - }
> -
> - return 0;
> + clk_set_rate(clk, ref);
> + return div | clk_idx << SCLK_510_SHIFT;
> }
>
> static const struct armada_ops armada510_ops = {
> @@ -85,6 +88,19 @@ static const struct armada_ops armada510_ops = {
> .compute_crtc_clock = armada510_compute_crtc_clock,
> };
>
> +static void release_clocks(struct armada_private *priv)
> +{
> + int i;
> + for (i = 0; i < ARMADA_MAX_CLOCK; i++) {
> + struct clk *clk = priv->clk[i];
> + if (!clk)
> + continue;
> +
> + clk_put(clk);
> + priv->clk[i] = NULL;
Yuck, really - if you really really need to use of_clk_get(), of_clk_get()
needs to be fixed to also have a devm_* counterpart. I'm sure lots of
people will appreciate whoever steps up and adds that.
> + }
> +}
> +
> static int armada_drm_load(struct drm_device *dev, unsigned long flags)
> {
> struct armada_private *priv;
> @@ -129,7 +145,7 @@ static int armada_drm_load(struct drm_device *dev, unsigned long flags)
>
> ret = priv->ops->init(priv, dev->dev);
> if (ret)
> - return ret;
> + goto err_buf;
>
> /* Mode setting support */
> drm_mode_config_init(dev);
> @@ -176,6 +192,7 @@ static int armada_drm_load(struct drm_device *dev, unsigned long flags)
> err_irq:
> drm_irq_uninstall(dev);
> err_kms:
> + release_clocks(priv);
> drm_mode_config_cleanup(dev);
> drm_mm_takedown(&priv->linear);
> err_buf:
> @@ -193,6 +210,7 @@ static int armada_drm_unload(struct drm_device *dev)
> drm_irq_uninstall(dev);
> drm_mode_config_cleanup(dev);
> drm_mm_takedown(&priv->linear);
> + release_clocks(priv);
> dev->dev_private = NULL;
>
> return 0;
> diff --git a/drivers/gpu/drm/armada/armada_hw.h b/drivers/gpu/drm/armada/armada_hw.h
> index 58d2a20..df59b5a 100644
> --- a/drivers/gpu/drm/armada/armada_hw.h
> +++ b/drivers/gpu/drm/armada/armada_hw.h
> @@ -193,11 +193,12 @@ enum {
> };
>
> /* For LCD_CFG_SCLK_DIV */
> +#define SCLK_510_SHIFT 30
> enum {
> - SCLK_510_AXI = 0x0 << 30, /* Armada 510 */
> - SCLK_510_EXTCLK0 = 0x1 << 30, /* Armada 510 */
> - SCLK_510_PLL = 0x2 << 30, /* Armada 510 */
> - SCLK_510_EXTCLK1 = 0x3 << 30, /* Armada 510 */
> + SCLK_510_AXI = 0x0 << SCLK_510_SHIFT, /* Armada 510 */
> + SCLK_510_EXTCLK0 = 0x1 << SCLK_510_SHIFT, /* Armada 510 */
> + SCLK_510_PLL = 0x2 << SCLK_510_SHIFT, /* Armada 510 */
> + SCLK_510_EXTCLK1 = 0x3 << SCLK_510_SHIFT, /* Armada 510 */
> SCLK_DIV_CHANGE = 1 << 29,
> SCLK_16X_AHB = 0x0 << 28, /* Armada 16x */
> SCLK_16X_PCLK = 0x1 << 28, /* Armada 16x */
> --
> 1.8.1.4
>
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