RE: [PATCH] drm/display: Increase DP_RECEIVER_CAP_SIZE from 15 to 16 bytes

["Cavitt, Jonathan" <jonathan.cavitt@intel.com>]

-----Original Message-----
From: Almahallawy, Khaled <khaled.almahallawy@intel.com> 
Sent: Wednesday, July 2, 2025 3:39 PM
To: dri-devel@lists.freedesktop.org; intel-gfx@lists.freedesktop.org; intel-xe@lists.freedesktop.org
Cc: Almahallawy, Khaled <khaled.almahallawy@intel.com>; Shankar, Uma <uma.shankar@intel.com>; Sean Paul <seanpaul@chromium.org>; Cavitt, Jonathan <jonathan.cavitt@intel.com>; Nikula, Jani <jani.nikula@intel.com>
Subject: [PATCH] drm/display: Increase DP_RECEIVER_CAP_SIZE from 15 to 16 bytes
> 
> Several Link Layer tests (4.2.2.1-2, 4.2.2.7-9) fail because DPTX doesn't
> read DPCD ADAPTER_CAP addresses (0x000F and 0x220F).
> 
> 4.2.2.1 test states [1]:
> "Fail1: Source DUT failed to read the DPCD Receiver Capability field
> (DPCD:00000h:0000Fh) through AUX_CH before link training."
> 
> 4.2.2.2 test states [1]:
> "Fail2: Source DUT failed to read the DPCD Extended Receiver Capability
> field (DPCD:02200h:0220Fh) through AUX_CH before link training."
> 
> Additionally, the spec [2] states:
> "The Source device shall respond to Hot Plug event/Hot Re-plug event by
> first reading DPCD Link/Sink Device Status registers at DPCD 00200h
> through 00205h -or- DPCD 02002h through 0200Fh. If the link is unstable
> or lost, the Source device then reads the DPCD Receiver Capabilities
> registers at DPCD 00000h through 0000Fh to determine the appropriate
> information needed to train the link. The Source device shall then
> initiate link training."
> 
> Increasing DP_RECEIVER_CAP_SIZE by 1 byte ensures passing the test
> conditions for these link layer tests.
> 
> [1]: DisplayPort v2.1 Link Layer Compliance Test Specification
> sections 4.2.2.1 & 4.2.2.2
> [2]: DisplayPort Standard v2.1 - Sec 5.1.4 Source Device Behavior
> upon HPD Pulse Detection
> 
> Cc: Uma Shankar <uma.shankar@intel.com>
> Cc: Sean Paul <seanpaul@chromium.org>
> Cc: Jonathan Cavitt <jonathan.cavitt@intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Signed-off-by: Khaled Almahallawy <khaled.almahallawy@intel.com>

LGTM.
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
-Jonathan Cavitt

> ---
>  include/drm/display/drm_dp.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/drm/display/drm_dp.h b/include/drm/display/drm_dp.h
> index 811e9238a77c..960c9757ba76 100644
> --- a/include/drm/display/drm_dp.h
> +++ b/include/drm/display/drm_dp.h
> @@ -1681,7 +1681,7 @@ enum drm_dp_phy {
>  #define DP_LINK_STATUS_SIZE	   6
>  
>  #define DP_BRANCH_OUI_HEADER_SIZE	0xc
> -#define DP_RECEIVER_CAP_SIZE		0xf
> +#define DP_RECEIVER_CAP_SIZE		0x10
>  #define DP_DSC_RECEIVER_CAP_SIZE        0x10 /* DSC Capabilities 0x60 through 0x6F */
>  #define EDP_PSR_RECEIVER_CAP_SIZE	2
>  #define EDP_DISPLAY_CTL_CAP_SIZE	5
> -- 
> 2.43.0
> 
>