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

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Oct 06, 2015 at 02:41:44PM +0300, Ville Syrjälä wrote:
> 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.

Hm right, cdlck is in the top-level power domain. Added fun is that with
dmc the firmware is supposed to handle it. Messy :(
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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