[Intel-gfx] [PATCH] drm/i915/skl: Init cdclk in the driver rather than relying on pre-os

[Daniel Vetter]

On Tue, Oct 06, 2015 at 04:33:43PM +0530, Kumar, Shobhit wrote:
> On 10/06/2015 04:11 PM, Imre Deak wrote:
> >On ti, 2015-10-06 at 15:26 +0530, Kumar, Shobhit wrote:
> >>On 10/05/2015 09:05 PM, Imre Deak wrote:
> >>>On ma, 2015-10-05 at 20:52 +0530, Shobhit Kumar wrote:
> >>>>Mostly reuse what is programmed by pre-os, but in case there is no
> >>>>pre-os initialization, init the cdclk with the default value.
> >>>>
> >>>>Cc: Imre Deak <imre.deak at intel.com>
> >>>>Signed-off-by: Shobhit Kumar <shobhit.kumar at intel.com>
> >>>>---
> >>>>   drivers/gpu/drm/i915/intel_ddi.c | 6 ++----
> >>>>   1 file changed, 2 insertions(+), 4 deletions(-)
> >>>>
> >>>>diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> >>>>index 2d3cc82..675c60d 100644
> >>>>--- a/drivers/gpu/drm/i915/intel_ddi.c
> >>>>+++ b/drivers/gpu/drm/i915/intel_ddi.c
> >>>>@@ -2947,10 +2947,8 @@ void intel_ddi_pll_init(struct drm_device *dev)
> >>>>
> >>>>   		cdclk_freq = dev_priv->display.get_display_clock_speed(dev);
> >>>>   		dev_priv->skl_boot_cdclk = cdclk_freq;
> >>>>-		if (!(I915_READ(LCPLL1_CTL) & LCPLL_PLL_ENABLE))
> >>>>-			DRM_ERROR("LCPLL1 is disabled\n");
> >>>>-		else
> >>>>-			intel_display_power_get(dev_priv, POWER_DOMAIN_PLLS);
> >>>>+
> >>>>+		skl_init_cdclk(dev_priv);
> >>>
> >>>How does this prevent changing the clock if BIOS did enable some output?
> >>>We shouldn't change the clock in that case.
> >>
> >>In that case it will try to re-apply the same clock that BIOS enabled.
> >>Not sure if this is allowed, but I checked the cdclock change sequence
> >>and it is mostly followed in skl_init_cdclk.
> >>In my tests where BIOS does enable this, I faced no issues in
> >>initializing again in driver.
> >
> >The first step in that sequence:
> >"Disable all display engine functions using the full mode set disable
> >sequence on all pipes, ports, and planes."
> 
> Oh, yeah, I again made mistake of assuming that display is not enabled in
> the first place. You are right, though it works if I change the clock again.
> 
> >
> >So the problem is not that the PLL itself may be enabled here (as BIOS
> >left it), but that some output is also enabled.
> 
> Yes.
> 
> >
> >>I have noticed on some pre-os this value is programmed correctly except
> >>for the decimal part. That causes AUX transactions to fail on SKl. That
> >>is what triggered this patch actually. So other way is to completely
> >>validate the value in get_display_clock_speed instead of bit[28:26] and
> >>then if wrong then only do the cdclk init.
> >
> >I think we'd need to detect at this point if outputs are enabled and
> >only attempt to work around the above BIOS problem if this is not the
> >case. Alternatively you could also disable the active outputs as a first
> >step.
> 
> Ok, let me detect if any output is enabled by BIOS and accordingly
> initialize cdclk.

These kind of fixiups should be done after the hw state readout. We
already have sanitize_crtc/pll/encoder functions, probably best if we add
a sanitize_cdclk or similar for this at the very end of the hw state
sanitize sequence.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch