Re: [Intel-gfx] [PATCH RESEND 5/7] drm/i915/mst: read link status only when requested by sink in ESI

["Shankar, Uma" <uma.shankar@intel.com>]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of Jani Nikula
> Sent: Wednesday, January 12, 2022 4:33 PM
> To: intel-gfx@lists.freedesktop.org
> Cc: Nikula, Jani <jani.nikula@intel.com>
> Subject: [Intel-gfx] [PATCH RESEND 5/7] drm/i915/mst: read link status only when
> requested by sink in ESI
> 
> The link service irq vector in DPCD 0x2005 contains the link status changed bit to
> indicate the status should be checked. Only read and check the link status when
> requested by the sink.
> 
> This also reduces the confusion around the buffer size for the combined ESI and link
> status. Alas, we still need to take into account that all link status helpers expect a
> buffer of DP_LINK_STATUS_SIZE (6) while the link status in ESI only has 4 bytes.

Looks Good to me.
Reviewed-by: Uma Shankar <uma.shankar@intel.com>

> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 41 +++++++++++--------------
>  1 file changed, 18 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> b/drivers/gpu/drm/i915/display/intel_dp.c
> index 5a7976768b06..d8a0ba3a14b7 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -73,8 +73,6 @@
>  #include "intel_vdsc.h"
>  #include "intel_vrr.h"
> 
> -#define DP_DPRX_ESI_LEN 14
> -
>  /* DP DSC throughput values used for slice count calculations KPixels/s */
>  #define DP_DSC_PEAK_PIXEL_RATE			2720000
>  #define DP_DSC_MAX_ENC_THROUGHPUT_0		340000
> @@ -2814,11 +2812,9 @@ intel_dp_configure_mst(struct intel_dp *intel_dp)  }
> 
>  static bool
> -intel_dp_get_sink_irq_esi(struct intel_dp *intel_dp, u8 *sink_irq_vector)
> +intel_dp_get_sink_irq_esi(struct intel_dp *intel_dp, u8 *esi)
>  {
> -	return drm_dp_dpcd_read(&intel_dp->aux, DP_SINK_COUNT_ESI,
> -				sink_irq_vector, DP_DPRX_ESI_LEN) ==
> -		DP_DPRX_ESI_LEN;
> +	return drm_dp_dpcd_read(&intel_dp->aux, DP_SINK_COUNT_ESI, esi, 4) ==
> +4;
>  }
> 
>  static bool intel_dp_ack_sink_irq_esi(struct intel_dp *intel_dp, u8 esi[4]) @@ -
> 3639,12 +3635,22 @@ intel_dp_mst_hpd_irq(struct intel_dp *intel_dp, u8 *esi, bool
> *handled)
>  	}
>  }
> 
> -static bool intel_dp_mst_link_status(struct intel_dp *intel_dp, u8 *esi)
> +static bool intel_dp_mst_link_status(struct intel_dp *intel_dp)
>  {
>  	struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
>  	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
> +	u8 link_status[DP_LINK_STATUS_SIZE] = {};
> +	const size_t esi_link_status_size = DP_LINK_STATUS_SIZE - 2;
> +
> +	if (drm_dp_dpcd_read(&intel_dp->aux, DP_LANE0_1_STATUS_ESI,
> link_status,
> +			     esi_link_status_size) != esi_link_status_size) {
> +		drm_err(&i915->drm,
> +			"[ENCODER:%d:%s] Failed to read link status\n",
> +			encoder->base.base.id, encoder->base.name);
> +		return false;
> +	}
> 
> -	if (!drm_dp_channel_eq_ok(&esi[10], intel_dp->lane_count)) {
> +	if (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count)) {
>  		drm_dbg_kms(&i915->drm,
>  			    "[ENCODER:%d:%s] channel EQ not ok, retraining\n",
>  			    encoder->base.base.id, encoder->base.name); @@ -
> 3676,18 +3682,7 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
>  	drm_WARN_ON_ONCE(&i915->drm, intel_dp->active_mst_links < 0);
> 
>  	for (;;) {
> -		/*
> -		 * The +2 is because DP_DPRX_ESI_LEN is 14, but we then
> -		 * pass in "esi+10" to drm_dp_channel_eq_ok(), which
> -		 * takes a 6-byte array. So we actually need 16 bytes
> -		 * here.
> -		 *
> -		 * Somebody who knows what the limits actually are
> -		 * should check this, but for now this is at least
> -		 * harmless and avoids a valid compiler warning about
> -		 * using more of the array than we have allocated.
> -		 */
> -		u8 esi[DP_DPRX_ESI_LEN+2] = {};
> +		u8 esi[4] = {};
>  		bool handled;
> 
>  		if (!intel_dp_get_sink_irq_esi(intel_dp, esi)) { @@ -3700,9 +3695,9
> @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
> 
>  		drm_dbg_kms(&i915->drm, "DPRX ESI: %4ph\n", esi);
> 
> -		/* check link status - esi[10] = 0x200c */
> -		if (intel_dp->active_mst_links > 0 && link_ok) {
> -			if (!intel_dp_mst_link_status(intel_dp, esi))
> +		if (intel_dp->active_mst_links > 0 && link_ok &&
> +		    esi[3] & LINK_STATUS_CHANGED) {
> +			if (!intel_dp_mst_link_status(intel_dp))
>  				link_ok = false;
>  		}
> 
> --
> 2.30.2