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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Oct 06, 2015 at 01:19:52PM +0200, Daniel Vetter wrote:
> 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@intel.com>
> > >>>>Signed-off-by: Shobhit Kumar <shobhit.kumar@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.

Can't be done if we already need a somewhat sane cdclk for the
eDP AUX probing and whatnot.

For actually enabling the cdclk for pushing pixels, we wouldn't need
to do anything except actually plug ia a calc_cdclk for SKL. No idea
why we're not doing that currently. Some extra care may be needed
due to the eDP DPLL0 usag IIRC.

> -Daniel
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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-- 
Ville Syrjälä
Intel OTC
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