[PATCH 6/9] drm/msm/dp: Work around bogus maximum link rate

[Xilin Wu]

On 2025/7/15 01:35:42, Dale Whinham wrote:
> From: Jérôme de Bretagne <jerome.debretagne at gmail.com>
> 
> The OLED display in the Surface Pro 11 reports a maximum link rate of
> zero in its DPCD, causing it to fail to probe correctly.
> 
> The Surface Pro 11's DSDT table contains some XML with an
> "EDPOverrideDPCDCaps" block that defines the max link rate as 0x1E
> (8.1Gbps/HBR3).
> 
> Add a quirk to conditionally override the max link rate if its value
> is zero specifically for this model.
> 
> Signed-off-by: Jérôme de Bretagne <jerome.debretagne at gmail.com>
> Signed-off-by: Dale Whinham <daleyo at gmail.com>
> ---
>   drivers/gpu/drm/msm/dp/dp_panel.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_panel.c b/drivers/gpu/drm/msm/dp/dp_panel.c
> index 4e8ab75c771b..b2e65b987c05 100644
> --- a/drivers/gpu/drm/msm/dp/dp_panel.c
> +++ b/drivers/gpu/drm/msm/dp/dp_panel.c
> @@ -11,6 +11,8 @@
>   #include <drm/drm_of.h>
>   #include <drm/drm_print.h>
>   
> +#include <linux/dmi.h>
> +
>   #define DP_MAX_NUM_DP_LANES	4
>   #define DP_LINK_RATE_HBR2	540000 /* kbytes */
>   
> @@ -58,6 +60,17 @@ static int msm_dp_panel_read_dpcd(struct msm_dp_panel *msm_dp_panel)
>   	if (rc)
>   		return rc;
>   
> +	/*
> +	 * for some reason the ATNA30DW01-1 OLED panel in the Surface Pro 11
> +	 * reports a max link rate of 0 in the DPCD. Fix it to match the
> +	 * EDPOverrideDPCDCaps string found in the ACPI DSDT
> +	 */
> +	if (dpcd[DP_MAX_LINK_RATE] == 0 &&
> +	    dmi_match(DMI_SYS_VENDOR, "Microsoft Corporation") &&
> +	    dmi_match(DMI_PRODUCT_NAME, "Microsoft Surface Pro, 11th Edition")) {
> +		dpcd[1] = DP_LINK_BW_8_1;
> +	}
> +

My Galaxy Book4 Edge with the ATNA60CL07-0 panel also reports a max link 
rate of 0. But I think eDP v1.4 panels need a different way to retrieve 
supported links rates, which could be found in the amdgpu [1], i915 [2] 
and nouveau [3] drivers.

[1]: 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c#n2098
[2]: 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/gpu/drm/i915/display/intel_dp.c#n4281
[3]: 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/gpu/drm/nouveau/nouveau_dp.c#n101


>   	msm_dp_panel->vsc_sdp_supported = drm_dp_vsc_sdp_supported(panel->aux, dpcd);
>   	link_info = &msm_dp_panel->link_info;
>   	link_info->revision = dpcd[DP_DPCD_REV];


-- 
Best regards,
Xilin Wu <sophon at radxa.com>