Re: [Intel-gfx] [PATCH 2/4] drm/dp: use more of the extended receiver cap

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

On Wed, 25 Aug 2021, Jani Nikula <jani.nikula@intel.com> wrote:
> On Thu, 19 Aug 2021, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
>> On Fri, Aug 13, 2021 at 01:43:20PM +0300, Jani Nikula wrote:
>>> Extend the use of extended receiver cap at 0x2200 to cover
>>> MAIN_LINK_CHANNEL_CODING_CAP in 0x2206, in case an implementation hides
>>> the DP 2.0 128b/132b channel encoding cap.
>>> 
>>> Cc: Manasi Navare <manasi.d.navare@intel.com>
>>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>>> ---
>>>  drivers/gpu/drm/drm_dp_helper.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>> 
>>> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
>>> index 9b2a2961fca8..9389f92cb944 100644
>>> --- a/drivers/gpu/drm/drm_dp_helper.c
>>> +++ b/drivers/gpu/drm/drm_dp_helper.c
>>> @@ -608,7 +608,7 @@ static u8 drm_dp_downstream_port_count(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
>>>  static int drm_dp_read_extended_dpcd_caps(struct drm_dp_aux *aux,
>>>  					  u8 dpcd[DP_RECEIVER_CAP_SIZE])
>>>  {
>>> -	u8 dpcd_ext[6];
>>> +	u8 dpcd_ext[DP_MAIN_LINK_CHANNEL_CODING + 1];
>>
>> Why are we even reading less of this than the normal receiver caps?
>
> Good question. I forget my reasoning to only extend to what might affect
> this use case. Should we extend to the size of the usual receiver caps?

Ah, there was a previous discussion [1] with Lyude (Cc'd).

BR,
Jani.


[1] https://patchwork.freedesktop.org/patch/msgid/20200901123226.4177-1-jani.nikula@intel.com


>
> BR,
> Jani.
>
>
>>
>>>  	int ret;
>>>  
>>>  	/*
>>> -- 
>>> 2.20.1

-- 
Jani Nikula, Intel Open Source Graphics Center