[PATCH] drm/dp: only accept valid DP_TRAINING_AUX_RD_INTERVAL values

[Manasi Navare]

Thanks for the patch. Masking the training AUX RD interval value to get
only the allowed values sounds of 0-4 is absolutely needed. Just one nit below:

On Fri, Mar 02, 2018 at 02:25:58PM -0800, matthew.s.atwood at intel.com wrote:
> From: Matt Atwood <matthew.s.atwood at intel.com>
> 
> For panels that do not follow Display Port specifications mask off invalid
> values for DP_TRAINING_AUX_RD_INTERVAL. Specification lists acceptable

It would be good to call out DP specification and a particular version number if possible
So DP 1.2 specification.

With that change,
Reviewed-by: Manasi Navare <manasi.d.navare at intel.com>

> values 0-4 all other values are reserved and bit 7 of DPCD 0x0000e
> describes another feature. Currently the code uses all of DPCD 0x0000e and
> can cause max wait for 1024 ms instead of 16 ms as specified table 2-158.
> This address is read for both clock recovery and channel equalization.
>

> Signed-off-by: Matt Atwood <matthew.s.atwood at intel.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 4 ++--
>  include/drm/drm_dp_helper.h     | 1 +
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index adf79be..a7e9b75 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -122,7 +122,7 @@ void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
>  	if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
>  		udelay(100);
>  	else
> -		mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
> +		mdelay((dpcd[DP_TRAINING_AUX_RD_INTERVAL] & DP_TRAINING_AUX_RD_MASK) * 4);
>  }
>  EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay);
>  
> @@ -130,7 +130,7 @@ void drm_dp_link_train_channel_eq_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
>  	if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
>  		udelay(400);
>  	else
> -		mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
> +		mdelay((dpcd[DP_TRAINING_AUX_RD_INTERVAL] & DP_TRAINING_AUX_RD_MASK) * 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..77ba003 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            0x7     /* 1.4 */
>  
>  #define DP_ADAPTER_CAP			    0x00f   /* 1.2 */
>  # define DP_FORCE_LOAD_SENSE_CAP	    (1 << 0)
> -- 
> 2.7.4
> 
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