[Intel-gfx] [PATCH] drm/i915/cnp: Ignore VBT request for know invalid DDC pin.

[Jani Nikula]

On Tue, 23 Jan 2018, Rodrigo Vivi <rodrigo.vivi at intel.com> wrote:
> On Tue, Jan 23, 2018 at 05:40:50PM +0000, Rodrigo Vivi wrote:
>> Let's ignore VBT request if the pin is clearly wrong.
>> 
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104139
>> Cc: Kai Heng Feng <kai.heng.feng at canonical.com>
>> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
>
> Reviewed-by: Radhakrishna Sripada <radhakrishna.sripada at intel.com>
> (f2f)
> thanks
>
> merged to dinq.

A bit too fast IMO. The bug report doesn't include the vbt dump which
you should *always* look at before making workarounds for vbt.

Also, see below.

>> ---
>>  drivers/gpu/drm/i915/intel_bios.c | 11 ++++++++---
>>  1 file changed, 8 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
>> index b0668202dc7e..95f0b310d656 100644
>> --- a/drivers/gpu/drm/i915/intel_bios.c
>> +++ b/drivers/gpu/drm/i915/intel_bios.c
>> @@ -1115,9 +1115,14 @@ static const u8 cnp_ddc_pin_map[] = {
>>  
>>  static u8 map_ddc_pin(struct drm_i915_private *dev_priv, u8 vbt_pin)
>>  {
>> -	if (HAS_PCH_CNP(dev_priv) &&
>> -	    vbt_pin > 0 && vbt_pin < ARRAY_SIZE(cnp_ddc_pin_map))
>> -		return cnp_ddc_pin_map[vbt_pin];
>> +	if (HAS_PCH_CNP(dev_priv)) {
>> +		if (vbt_pin > 0 && vbt_pin < ARRAY_SIZE(cnp_ddc_pin_map))
>> +			return cnp_ddc_pin_map[vbt_pin];
>> +		if (vbt_pin > GMBUS_PIN_4_CNP) {
>> +			DRM_DEBUG_KMS("Ignoring alternate pin: VBT claims DDC pin %d, which is not valid for this platform\n", vbt_pin);
>> +			return 0;
>> +		}

The original code was wrong in the sense that it would only do the
mapping if the provided vbt_pin was within bounds for CNP, and would
return the unmapped vbt_pin otherwise. Instead, I think you should
directly return 0 for out of bounds vbt_pin.

This change here is effectively the same, but more confusing. As if
there's a case where the vbt_pin can be both out of bounds, within CNP
pin limits, and should be returned unmapped. That can't happen, so
please make the code reflect that.

BR,
Jani.


>> +	}
>>  
>>  	return vbt_pin;
>>  }
>> -- 
>> 2.13.6
>> 
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-- 
Jani Nikula, Intel Open Source Technology Center