Re: [PATCH 02/20] drm/i915/dp_mst: Verify the link status always the same way

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 26 Jun 2025, Imre Deak <imre.deak@intel.com> wrote:
> From: Imre Deak <imre.deak@gmail.com>
>
> The MST link status should be always verified from the same DPCD
> registers after link training. Atm, both the legacy (0x202 - 0x205) and
> the ESI (0x200C - 0x200F) link status registers are used. Use always the
> latter ESI version of link status registers.
>
> Signed-off-by: Imre Deak <imre.deak@gmail.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 3f911c930a30b..ac7e08f485309 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5176,6 +5176,23 @@ intel_dp_handle_hdmi_link_status_change(struct intel_dp *intel_dp)
>  	}
>  }
>  
> +static bool
> +intel_dp_read_link_status(struct intel_dp *intel_dp, u8 link_status[DP_LINK_STATUS_SIZE])
> +{
> +	bool ret;
> +
> +	memset(link_status, 0, DP_LINK_STATUS_SIZE);
> +
> +	if (intel_dp_mst_active_streams(intel_dp) > 0)
> +		ret = drm_dp_dpcd_read_data(&intel_dp->aux, DP_LANE0_1_STATUS_ESI,
> +					    link_status, DP_LINK_STATUS_SIZE - 2) == 0;
> +	else
> +		ret = drm_dp_dpcd_read_phy_link_status(&intel_dp->aux, DP_PHY_DPRX,
> +						       link_status) == 0;

Please propagate the int instead of having "== 0" at the end of the
assignment.

I'm increasingly critical of bool returns for success/failure, because
they don't really mix well with 0 for success and negative values for
error.

> +
> +	return ret;
> +}
> +
>  static bool
>  intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
>  {
> @@ -5198,8 +5215,7 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
>  	if (intel_dp->link.force_retrain)
>  		return true;
>  
> -	if (drm_dp_dpcd_read_phy_link_status(&intel_dp->aux, DP_PHY_DPRX,
> -					     link_status) < 0)
> +	if (!intel_dp_read_link_status(intel_dp, link_status))
>  		return false;
>  
>  	/*

-- 
Jani Nikula, Intel