Re: [PATCH] drm/msm/dp: don't gate eDP on DP_SINK_COUNT

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 9/8/26 11:01 AM, 092vk wrote:
> msm_dp_display_prepare_link(), msm_dp_display_disable(), and
> msm_dp_hpd_unplug_handle() all treat dp->link->sink_count == 0 as
> "nothing is connected", and in msm_dp_display_prepare_link() this
> causes probe/enable to fail outright with -ENOTCONN.
> 
> This is correct for external DisplayPort, where a compliant sink is
> required to report a valid DP_SINK_COUNT over the AUX channel. It is
> not correct for eDP: some eDP sinks -- particularly fixed-format
> eDP-to-HDMI bridge chips with no downstream AUX-capable panel
> behind them -- never populate DP_SINK_COUNT with a nonzero value,
> even while otherwise participating normally in DPCD capability
> exchange and link training.
> 
> drm_dp_read_sink_count_cap() already accounts for this by excluding
> eDP connectors from the sink-count requirement for other DPCD-derived
> checks (msm_dp_bridge_detect() takes care). Apply the same exemption
> to the raw sink_count reads in this file via a small shared
> helper, so eDP outputs with a non-AUX-capable downstream sink are
> not treated as permanently disconnected.
> 
> Tested on a Qualcomm QCS6490-based board driving a fixed-format
> eDP-to-HDMI bridge IC (chrontel,ch7218a) with no negotiable
> DPCD-capable panel behind it; without this fix,
> msm_dp_display_prepare_link() unconditionally returns -ENOTCONN
> and the display never comes up.
> 
> Fixes: ca16db3d18cf ("drm/msm/dp: break up dp_display_enable into two parts")
> 
> Signed-off-by: 092vk <vk092kumar@gmail.com>
> ---

Hi, please use a known identity

https://docs.kernel.org/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin

Konrad