Re: [PATCH v2 5/6] drm/i915: Avoid a full port detection in the first eDP short pulse

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Oct 10, 2018 at 05:41:23PM -0700, José Roberto de Souza wrote:
> Some eDP panels do not set a valid sink count value and even for the
> ones that sets is should always be one for eDP, that is why it is not
> cached in intel_edp_init_dpcd().
> 
> But intel_dp_short_pulse() compares the old count with the read one
> if there is a mistmatch a full port detection will be executed, what
> was happening in the first short pulse interruption of eDP panels
> that sets sink count.
> 
> Instead of just skip the compasison for eDP panels, lets not read
> the sink count at all for eDP.
> 
> v2: the previous version of this patch was caching the sink count
> in intel_edp_init_dpcd() but I was pointed out by Ville a patch that
> handled a case of a eDP panel that do not set sink count
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 44 +++++++++++++++++++--------------
>  1 file changed, 26 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 13ff89be6ad6..1826d491efd7 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4034,8 +4034,6 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
>  static bool
>  intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  {
> -	u8 sink_count;
> -
>  	if (!intel_dp_read_dpcd(intel_dp))
>  		return false;
>  
> @@ -4045,25 +4043,35 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  		intel_dp_set_common_rates(intel_dp);
>  	}
>  
> -	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_SINK_COUNT, &sink_count) <= 0)
> -		return false;
> -
>  	/*
> -	 * Sink count can change between short pulse hpd hence
> -	 * a member variable in intel_dp will track any changes
> -	 * between short pulse interrupts.
> +	 * Some eDP panels do not set a valid value for sink count, that is why
> +	 * it don't care about read it here and in intel_edp_init_dpcd().

Can't quite parse that.

"Some eDP panels do not set a valid value
 for sink count, so we ignore it."

or something like that perhaps.

>  	 */
> -	intel_dp->sink_count = DP_GET_SINK_COUNT(sink_count);
> +	if (!intel_dp_is_edp(intel_dp)) {
> +		u8 count;
> +		ssize_t r;
>  
> -	/*
> -	 * SINK_COUNT == 0 and DOWNSTREAM_PORT_PRESENT == 1 implies that
> -	 * a dongle is present but no display. Unless we require to know
> -	 * if a dongle is present or not, we don't need to update
> -	 * downstream port information. So, an early return here saves
> -	 * time from performing other operations which are not required.
> -	 */
> -	if (!intel_dp_is_edp(intel_dp) && !intel_dp->sink_count)
> -		return false;
> +		r = drm_dp_dpcd_readb(&intel_dp->aux, DP_SINK_COUNT, &count);
> +		if (r < 1)
> +			return false;

My earlier suggestion was that we should keep reading this
anyway because some cts maybe required it. Would at least
avoid mixing in two functional changes into once patch.

> +
> +		/*
> +		 * Sink count can change between short pulse hpd hence
> +		 * a member variable in intel_dp will track any changes
> +		 * between short pulse interrupts.
> +		 */
> +		intel_dp->sink_count = DP_GET_SINK_COUNT(count);
> +
> +		/*
> +		 * SINK_COUNT == 0 and DOWNSTREAM_PORT_PRESENT == 1 implies that
> +		 * a dongle is present but no display. Unless we require to know
> +		 * if a dongle is present or not, we don't need to update
> +		 * downstream port information. So, an early return here saves
> +		 * time from performing other operations which are not required.
> +		 */
> +		if (!intel_dp->sink_count)
> +			return false;
> +	}
>  
>  	if (!drm_dp_is_branch(intel_dp->dpcd))
>  		return true; /* native DP sink */
> -- 
> 2.19.1

-- 
Ville Syrjälä
Intel
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