[Intel-gfx] [v2 1/6] i915/dp/fec: Cache the FEC_CAPABLE DPCD register

[Manasi Navare]

On Mon, Oct 15, 2018 at 02:50:32PM -0700, Anusha Srivatsa wrote:
> Similar to DSC DPCD registers, let us cache
> FEC_CAPABLE register to avoid using stale
> values. With this we can avoid aux reads
> everytime and instead read the cached values.
> 
> Suggested-by: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> Cc: Manasi Navare <manasi.d.navare at intel.com>
> Signed-off-by: Anusha Srivatsa <anusha.srivatsa at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c  | 8 ++++++++
>  drivers/gpu/drm/i915/intel_drv.h | 1 +
>  2 files changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index dcc5a207fcbd..8a0e0a0b26f6 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4163,8 +4163,10 @@ static void intel_dp_get_dsc_sink_cap(struct intel_dp *intel_dp)
>  	/*
>  	 *Clear the cached register set to avoid using stale values
>  	 * for the sinks that do not support DSC.
> +	 * Similarly, clear the cached FEC register.
>  	 */
>  	memset(intel_dp->dsc_dpcd, 0, sizeof(intel_dp->dsc_dpcd));
> +	memset(intel_dp->fec_dpcd, 0, sizeof(intel_dp->fec_dpcd));

Memset is an expensive opertaion for just a single value,
just set that to 0

>  
>  	/* Cache the DSC DPCD if eDP or DP rev >= 1.4 */
>  	if (intel_dp->dpcd[DP_DPCD_REV] >= 0x14 ||
> @@ -4179,6 +4181,12 @@ static void intel_dp_get_dsc_sink_cap(struct intel_dp *intel_dp)
>  			      (int)sizeof(intel_dp->dsc_dpcd),
>  			      intel_dp->dsc_dpcd);
>  	}
> +	/* FEC is supported only on DP 1.4 */
> +	if (!intel_dp_is_edp(intel_dp) && intel_dp->dpcd[DP_DPCD_REV] >= 0x14) {
> +		if (drm_dp_dpcd_readb(&intel_dp->aux, DP_FEC_CAPABILITY,
> +				      intel_dp->fec_dpcd) < 0)
> +			DRM_ERROR("Failed to read FEC DPCD register\n");
> +	}
>  }
>  
>  static bool
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 7b4af8cba279..b87ea052c9ca 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -1086,6 +1086,7 @@ struct intel_dp {
>  	uint8_t downstream_ports[DP_MAX_DOWNSTREAM_PORTS];
>  	uint8_t edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
>  	u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE];
> +	u8 fec_dpcd[1];

Why create an array for just 1 value, I think just a u8 fec_capable field
will suffice

Manasi

>  	/* source rates */
>  	int num_source_rates;
>  	const int *source_rates;
> -- 
> 2.17.1
>