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

Kumar, Shobhit shobhit.kumar at linux.intel.com
Tue Oct 6 05:43:52 PDT 2015

On 10/06/2015 05:49 PM, Daniel Vetter wrote:
> 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 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.
>> 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 :(

Yes, exactly. How about just adding verify_cdclk and calling in 
get_display_clock_speed to check if cdclk is programmed correctly along 
with related DPLL0 VCO settings for now. If all looks good, then skip 
else initialize. Now in that case if we have to initialize where do we 
get the cdclock to initialize with at this point ? Any default in VBT ? 
Or go with minimum by default and it can be bumped up later if needed.


> -Daniel

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