Re: [PATCH] drm/i915/skl: While sanitizing cdclock check the SWF18 as well

["Kumar, Shobhit" <shobhit.kumar@linux.intel.com>]

On 11/02/2015 10:07 PM, Thulasimani, Sivakumar wrote:
>
>
> On 11/2/2015 6:49 PM, Kumar, Shobhit wrote:
>> On 11/02/2015 06:40 PM, Jani Nikula wrote:
>>> On Mon, 02 Nov 2015, Shobhit Kumar <shobhit.kumar@intel.com> wrote:
>>>> SWF18 is set if the display has been intialized by the pre-os. It
>>>> also gives what configuration is enabled on which pipe. The DPLL and
>>>> CDCLK verification checks can fail as the pre-os does initialize the
>>>> DPLL for Audio codec initialization. So fisrt check if SWF18 is set and
>>>> then follow through with other DPLL and CDCLK verification.
>>>
>>> Can we universally trust all bios/gop/bootloader/whatnot to have
>>> initialized this? What if it's not set?
>>>
>>
>> As per my discussion with gop team, this has been enabled in main
>> stream for quite sometime including VLV, CHT, BDW, SKL+ and is common
>> for GOP/VBIOS across chrome/windows/android. So yes I think we can
>> universally trust as of now.
> This has been added since IVB timeframe and should be part of VBT spec.
> but i just encountered
> an issue in Android Charging OS where there is no modeset and is using
> the displays
> enabled by GOP/VBIOS. This patch might break such expectations.

Why would this break anything in Android charging UI. Basically this 
patch only says do cdclock sanitization if display is not enabled by 
pre-os. In this use case it is already enabled by GOP/VBIOS and the 
driver any way expects it to be programmed by pre-os in general. So in 
this scenario, the sanitization logic will not do anything at all 
because SWF18 will be set and CDCLOCK and DPLL will be properly enabled 
already and just return false. Fast-modeset should not be broken by this 
at all.

>>
>> Regards
>> Shobhit
>>
>>> BR,
>>> Jani.
>>>
>>>
>>>
>>>>
>>>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>>> Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
>>>> ---
>>>>   drivers/gpu/drm/i915/i915_reg.h      | 3 +++
>>>>   drivers/gpu/drm/i915/intel_display.c | 8 ++++++++
>>>>   2 files changed, 11 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/i915_reg.h
>>>> b/drivers/gpu/drm/i915/i915_reg.h
>>>> index 9ee9481..bd476ff 100644
>>>> --- a/drivers/gpu/drm/i915/i915_reg.h
>>>> +++ b/drivers/gpu/drm/i915/i915_reg.h
>>>> @@ -5006,6 +5006,9 @@ enum skl_disp_power_wells {
>>>>   #define SWF1(i)    (dev_priv->info.display_mmio_offset + 0x71410 +
>>>> (i) * 4)
>>>>   #define SWF3(i)    (dev_priv->info.display_mmio_offset + 0x72414 +
>>>> (i) * 4)
>>>>
>>>> +/* VBIOS flag for display initialized status */
>>>> +#define GEN6_SWF18  (dev_priv->info.display_mmio_offset + 0x4F060)
>>>> +
>>>>   /* Pipe B */
>>>>   #define _PIPEBDSL (dev_priv->info.display_mmio_offset + 0x71000)
>>>>   #define _PIPEBCONF (dev_priv->info.display_mmio_offset + 0x71008)
>>>> diff --git a/drivers/gpu/drm/i915/intel_display.c
>>>> b/drivers/gpu/drm/i915/intel_display.c
>>>> index 103cacb..0ecb35c 100644
>>>> --- a/drivers/gpu/drm/i915/intel_display.c
>>>> +++ b/drivers/gpu/drm/i915/intel_display.c
>>>> @@ -5761,6 +5761,14 @@ int skl_sanitize_cdclk(struct
>>>> drm_i915_private *dev_priv)
>>>>       uint32_t cdctl = I915_READ(CDCLK_CTL);
>>>>       int freq = dev_priv->skl_boot_cdclk;
>>>>
>>>> +    /*
>>>> +     * check if the pre-os intialized the display
>>>> +     * There is SWF18 scratchpad register defined which is set by the
>>>> +     * pre-os which can be used by the OS drivers to check the status
>>>> +     */
>>>> +    if ((I915_READ(GEN6_SWF18) & 0x00FFFF) == 0)
>>>> +        goto sanitize;
>>>> +
>>>>       /* Is PLL enabled and locked ? */
>>>>       if (!((lcpll1 & LCPLL_PLL_ENABLE) && (lcpll1 & LCPLL_PLL_LOCK)))
>>>>           goto sanitize;
>>>
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>
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