Re: [PATCH] drm/dp: Correctly mask DP_TRAINING_AUX_RD_INTERVAL values for DP 1.4

From: Rodrigo Vivi <rodrigo.vivi@intel.com>
To: matthew.s.atwood@intel.com
Cc: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/dp: Correctly mask DP_TRAINING_AUX_RD_INTERVAL values for DP 1.4
Date: Tue, 6 Mar 2018 15:24:49 -0800	[thread overview]
Message-ID: <20180306232449.GO15113@intel.com> (raw)
In-Reply-To: <1520361468-32087-1-git-send-email-matthew.s.atwood@intel.com>

On Tue, Mar 06, 2018 at 10:37:48AM -0800, matthew.s.atwood@intel.com wrote:
> From: Matt Atwood <matthew.s.atwood@intel.com>
> 
> DP_TRAINING_AUX_RD_INTERVAL with DP 1.3 spec changed bit scheme from 8
> bits to 7 bits in DPCD 0x000e. The 8th bit describes a new feature, for
> panels that use this new feature, this would cause a wait interval for
> clock recovery of at least 512 ms, much higher then spec maximum of 16 ms.
> This behavior is described in table 2-158 of DP 1.4 spec address 0000Eh.
> To avoid breaking panels that are not spec compliant we now warn on
> invalid values.
> 
> V2: commit title/message, masking all 7 bits, warn on out of spec values.

this approach is even better imho.

> 
> Signed-off-by: Matt Atwood <matthew.s.atwood@intel.com>

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

> ---
>  drivers/gpu/drm/drm_dp_helper.c | 18 ++++++++++++++----
>  include/drm/drm_dp_helper.h     |  1 +
>  2 files changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index adf79be..a718ccc 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -119,18 +119,28 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SI
>  EXPORT_SYMBOL(drm_dp_get_adjust_request_pre_emphasis);
>  
>  void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
> -	if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
> +	int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] & DP_TRAINING_AUX_RD_MASK;
> +
> +	if (rd_interval > 4)
> +		DRM_DEBUG_KMS("AUX interval %d, out of range (max 4)", rd_interval);
> +
> +	if (rd_interval == 0)
>  		udelay(100);
>  	else
> -		mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
> +		mdelay(rd_interval * 4);
>  }
>  EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay);
>  
>  void drm_dp_link_train_channel_eq_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
> -	if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
> +	int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] & DP_TRAINING_AUX_RD_MASK;
> +
> +	if (rd_interval > 4)
> +		DRM_DEBUG_KMS("AUX interval %d, out of range (max 4)", rd_interval);
> +
> +	if (rd_interval == 0)
>  		udelay(400);
>  	else
> -		mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
> +		mdelay(rd_interval * 4);
>  }
>  EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay);
>  
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index da58a42..f80acf1 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -118,6 +118,7 @@
>  # define DP_DPCD_DISPLAY_CONTROL_CAPABLE     (1 << 3) /* edp v1.2 or higher */
>  
>  #define DP_TRAINING_AUX_RD_INTERVAL         0x00e   /* XXX 1.2? */
> +# define DP_TRAINING_AUX_RD_MASK            0x7F     /* 1.3 */
>  
>  #define DP_ADAPTER_CAP			    0x00f   /* 1.2 */
>  # define DP_FORCE_LOAD_SENSE_CAP	    (1 << 0)
> -- 
> 2.7.4
> 
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