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

From: "Kumar, Shobhit" <shobhit.kumar@linux.intel.com>
To: Jani Nikula <jani.nikula@linux.intel.com>,
	Shobhit Kumar <shobhit.kumar@intel.com>,
	intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915/skl: While sanitizing cdclock check the SWF18 as well
Date: Mon, 2 Nov 2015 18:49:50 +0530	[thread overview]
Message-ID: <563762F6.7050603@linux.intel.com> (raw)
In-Reply-To: <87pozso8bv.fsf@intel.com>

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.

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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