Re: [PATCH] drm/i915: Clear the VBT defaults for unused ports

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 03 Mar 2017, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Fri, Mar 03, 2017 at 05:01:42AM -0800, Manasi Navare wrote:
>> If during VBT parsing we find that the port is unused,
>> the driver code just bails out without clearing the
>> defaults for that port. This can cause failures down
>> the path through link training for unused Port.
>> This patch fixes this issue by clearing the defaults
>> before bailing out from the VBT parsing function.
>> 
>> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
>> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_bios.c | 10 ++++++++--
>>  1 file changed, 8 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
>> index e144f03..3ac3d24 100644
>> --- a/drivers/gpu/drm/i915/intel_bios.c
>> +++ b/drivers/gpu/drm/i915/intel_bios.c
>> @@ -1148,9 +1148,15 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv, enum port port,
>>  			}
>>  		}
>>  	}
>> -	if (!child)
>> -		return;
>> +	if (!child) {
>> +		/* Clear the DDI VBT Port info values */
>> +		info->supports_dvi = 0;
>> +		info->supports_hdmi = 0;
>> +		info->supports_dp = 0;
>> +		info->supports_edp = 0;
>
> I would s/0/false/ here. Although they are apparently of type 'uint8_t:1'.
> As a followup someone might want to s/uint8_t:1/bool:1/ the definitions
> so that the compiler will protect us against values >1 when we assign
> these.
>
> Otherwise lgtm. And based on a cursory glance the bogus port A has now
> disappaered from the ci results on fi-skl-6700k, so looks like my
> analysis of the problem was correct.
>
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Bikeshedding after review...

I think the approach here is a bit magical, first setting defaults on
all platforms, then removing same defaults on platforms that a) are DDI,
b) have VBT, c) have a high enough VBT revision, and d) do not have
child devices.

I think I'd go with simplicity, and split out a function from
init_vbt_defaults() to be called on platforms without VBT. It would
initially just contain the loop to initialize

	info->supports_dvi = (port != PORT_A && port != PORT_E);
	info->supports_hdmi = info->supports_dvi;
	info->supports_dp = (port != PORT_E);


BR,
Jani.


>
>>  
>> +		return;
>> +	}
>>  	aux_channel = child->common.aux_channel;
>>  	ddc_pin = child->common.ddc_pin;
>>  
>> -- 
>> 2.1.4

-- 
Jani Nikula, Intel Open Source Technology Center
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