[PATCH] drm/i915/dp: Limit SST link rate to <=8.1Gbps

[PATCH] drm/i915/dp: Limit SST link rate to <=8.1Gbps

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala@linux.intel.com>

Limit the link rate to HBR3 or below (<=8.1Gbps) in SST mode.
UHBR (10Gbps+) link rates require 128b/132b channel encoding
which we have not yet hooked up into the SST/no-sideband codepaths.

Cc: stable@vger.kernel.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index ab415f41924d..5045c34a16be 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -2356,6 +2356,9 @@ intel_dp_compute_config_limits(struct intel_dp *intel_dp,
 	limits->min_rate = intel_dp_common_rate(intel_dp, 0);
 	limits->max_rate = intel_dp_max_link_rate(intel_dp);
 
+	/* FIXME 128b/132b SST support missing */
+	limits->max_rate = min(limits->max_rate, 810000);
+
 	limits->min_lane_count = 1;
 	limits->max_lane_count = intel_dp_max_lane_count(intel_dp);
 
-- 
2.43.0

Re: [PATCH] drm/i915/dp: Limit SST link rate to <=8.1Gbps

[Jani Nikula]

On Thu, 08 Feb 2024, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Limit the link rate to HBR3 or below (<=8.1Gbps) in SST mode.
> UHBR (10Gbps+) link rates require 128b/132b channel encoding
> which we have not yet hooked up into the SST/no-sideband codepaths.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

My bad.

I guess this is the smallest most isolated fix for stable.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>



> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index ab415f41924d..5045c34a16be 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -2356,6 +2356,9 @@ intel_dp_compute_config_limits(struct intel_dp *intel_dp,
>  	limits->min_rate = intel_dp_common_rate(intel_dp, 0);
>  	limits->max_rate = intel_dp_max_link_rate(intel_dp);
>  
> +	/* FIXME 128b/132b SST support missing */
> +	limits->max_rate = min(limits->max_rate, 810000);
> +
>  	limits->min_lane_count = 1;
>  	limits->max_lane_count = intel_dp_max_lane_count(intel_dp);

-- 
Jani Nikula, Intel