[PATCH v1 0/1] drm/dp_mst: Use the correct max source link rate for i915

[PATCH v1 0/1] drm/dp_mst: Use the correct max source link rate for i915

[Nikola Cornij]

This is a follow-up change to fix incorrectly used max link rate source
capability at MST init time.

Change history:

v1:
  - Initial

Nikola Cornij (1):
  drm/dp_mst: Use the correct max source link rate for i915

 drivers/gpu/drm/i915/display/intel_dp_mst.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

-- 
2.25.1

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[PATCH v1 1/1] drm/dp_mst: Use the correct max source link rate for i915

[Nikola Cornij]

[why]
Previously used value was not safe to provide the correct value, i.e. it
could be 0 if not not configured, leading to no MST on this platform.

[how]
Do not use the value from BIOS, but from the structure populated at
encoder initialization time.

Fixes: 98025a62cb00 ("drm/dp_mst: Use Extended Base Receiver Capability DPCD space")
Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
---
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index bf7f8487945c..01a0ed99988f 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -942,7 +942,6 @@ intel_dp_mst_encoder_init(struct intel_digital_port *dig_port, int conn_base_id)
 	struct intel_dp *intel_dp = &dig_port->dp;
 	enum port port = dig_port->base.port;
 	int ret;
-	int bios_max_link_rate;
 
 	if (!HAS_DP_MST(i915) || intel_dp_is_edp(intel_dp))
 		return 0;
@@ -957,11 +956,11 @@ intel_dp_mst_encoder_init(struct intel_digital_port *dig_port, int conn_base_id)
 
 	/* create encoders */
 	intel_dp_create_fake_mst_encoders(dig_port);
-	bios_max_link_rate = intel_bios_dp_max_link_rate(&dig_port->base);
 	ret = drm_dp_mst_topology_mgr_init(&intel_dp->mst_mgr, &i915->drm,
 					   &intel_dp->aux, 16, 3,
 					   (u8)dig_port->max_lanes,
-					   (u8)(bios_max_link_rate / 27000), conn_base_id);
+					   (u8)(intel_dp->source_rates[intel_dp->num_source_rates - 1] / 27000),
+					   conn_base_id);
 	if (ret)
 		return ret;
 
-- 
2.25.1

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Re: [PATCH v1 1/1] drm/dp_mst: Use the correct max source link rate for i915

[Lyude Paul]

On Fri, 2021-04-30 at 17:22 -0400, Nikola Cornij wrote:
> [why]
> Previously used value was not safe to provide the correct value, i.e. it
> could be 0 if not not configured, leading to no MST on this platform.
> 
> [how]
> Do not use the value from BIOS, but from the structure populated at
> encoder initialization time.
> 
> Fixes: 98025a62cb00 ("drm/dp_mst: Use Extended Base Receiver Capability DPCD
> space")
> Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index bf7f8487945c..01a0ed99988f 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -942,7 +942,6 @@ intel_dp_mst_encoder_init(struct intel_digital_port
> *dig_port, int conn_base_id)
>         struct intel_dp *intel_dp = &dig_port->dp;
>         enum port port = dig_port->base.port;
>         int ret;
> -       int bios_max_link_rate;
>  
>         if (!HAS_DP_MST(i915) || intel_dp_is_edp(intel_dp))
>                 return 0;
> @@ -957,11 +956,11 @@ intel_dp_mst_encoder_init(struct intel_digital_port
> *dig_port, int conn_base_id)
>  
>         /* create encoders */
>         intel_dp_create_fake_mst_encoders(dig_port);
> -       bios_max_link_rate = intel_bios_dp_max_link_rate(&dig_port->base);
>         ret = drm_dp_mst_topology_mgr_init(&intel_dp->mst_mgr, &i915->drm,
>                                            &intel_dp->aux, 16, 3,
>                                            (u8)dig_port->max_lanes,
> -                                          (u8)(bios_max_link_rate / 27000),
> conn_base_id);
> +                                          (u8)(intel_dp-
> >source_rates[intel_dp->num_source_rates - 1] / 27000),
> +                                          conn_base_id);

This line is kind of long, I'd say we should just store the max link rate in a
local variable like max_link_rate, then just pass that to
drm_dp_mst_topology_mgr_init()

Also, the commit message should probably be:

drm/i915: Use the correct max source link rate for MST

With those two things fixed:

Reviewed-by: Lyude Paul <lyude@redhat.com>

>         if (ret)
>                 return ret;
>  

-- 
Sincerely,
   Lyude Paul (she/her)
   Software Engineer at Red Hat
   
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