[Intel-gfx] [PATCH] drm/dp: Correctly mask DP_TRAINING_AUX_RD_INTERVAL values for DP 1.4

[Rodrigo Vivi]

On Thu, Mar 15, 2018 at 02:08:51PM -0700, matthew.s.atwood at intel.com wrote:
> From: Matt Atwood <matthew.s.atwood at intel.com>
> 
> DP_TRAINING_AUX_RD_INTERVAL with DP 1.3 spec changed bit scheeme from 8
> bits to 7 in DPCD 0x000e. The 8th bit is used to identify extended
> receiver capabilities. For panels that use this new feature wait interval
> would be increased by 512 ms, when spec is max 16 ms. This behavior is
> described in table 2-158 of DP 1.4 spec address 0000eh.
> 
> With the introduction of DP 1.4 spec main link clock recovery was
> standardized to 100 us regardless of TRAINING_AUX_RD_INTERVAL value.
> 
> To avoid breaking panels that are not spec compiant we now warn on
> invalid values.
> 
> V2: commit title/message, masking all 7 bits, warn on out of spec values.
> V3: commit message, make link train clock recovery follow DP 1.4 spec.
> V4: style changes
> V5: typo
> V6: print statement revisions, DP_REV to DPCD_REV, comment correction
> V7: typo
> V8: Style

thanks :)

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

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



> ---
>  drivers/gpu/drm/drm_dp_helper.c | 22 ++++++++++++++++++----
>  include/drm/drm_dp_helper.h     |  6 ++++++
>  2 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index adf79be..6bee2df 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -119,18 +119,32 @@ 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)\n",
> +			      rd_interval);
> +
> +	if (rd_interval == 0 || dpcd[DP_DPCD_REV] >= DPCD_REV_14)
>  		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)\n",
> +			      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..8c59ce4 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -64,6 +64,11 @@
>  /* AUX CH addresses */
>  /* DPCD */
>  #define DP_DPCD_REV                         0x000
> +# define DPCD_REV_10                        0x10
> +# define DPCD_REV_11                        0x11
> +# define DPCD_REV_12                        0x12
> +# define DPCD_REV_13                        0x13
> +# define DPCD_REV_14                        0x14
>  
>  #define DP_MAX_LINK_RATE                    0x001
>  
> @@ -118,6 +123,7 @@
>  # 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    /* XXX 1.2? */
>  
>  #define DP_ADAPTER_CAP			    0x00f   /* 1.2 */
>  # define DP_FORCE_LOAD_SENSE_CAP	    (1 << 0)
> -- 
> 2.7.4
> 
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