Re: [PATCH 1/4] drm/i915/dp_mst: Fix connector initialization in intel_dp_add_mst_connector()

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Fri, Nov 15, 2024 at 06:41:56PM +0200, Imre Deak wrote:
> The connector initialization in intel_dp_add_mst_connector() depends on
> the device pointer in connector to be valid, at least by connector
> debug printing. The device pointer is initialized by drm_connector_init(),
> however that function also exposes the connector to in-kernel users,
> which can't be done before the connector is fully initialized. For now
> make sure the device pointer is valid before it's used, until a
> follow-up change moving this to DRM core.
> 
> This issue was revealed by the commit in the Fixes: line below, before
> which the above debug printing checked and handled a NULL device pointer
> gracefully in DRM core.
> 
> Cc: Jani Nikula <jani.nikula@intel.com>
> Fixes: 529798bd786a ("drm/i915/mst: convert to struct intel_display")

This is awkward. This patch actually removes callers of base.dev.
I don't see how that it could be causing this new null dereference.

> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12799

But well, trusting more the tests then my eyes, let's move forward.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index df7edcfe885b6..f058360a26413 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -1727,6 +1727,16 @@ static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
>  
>  	intel_dp_init_modeset_retry_work(intel_connector);
>  
> +	/*
> +	 * TODO: The following drm_connector specific initialization belongs
> +	 * to DRM core, however it happens atm too late in
> +	 * drm_connector_init(). That function will also expose the connector
> +	 * to in-kernel users, so it can't be called until the connector is
> +	 * sufficiently initialized; init the device pointer used by the
> +	 * following DSC setup, until a fix moving this to DRM core.
> +	 */
> +	intel_connector->base.dev = mgr->dev;
> +
>  	intel_connector->dp.dsc_decompression_aux = drm_dp_mst_dsc_aux_for_port(port);
>  	intel_dp_mst_read_decompression_port_dsc_caps(intel_dp, intel_connector);
>  	intel_connector->dp.dsc_hblank_expansion_quirk =
> -- 
> 2.44.2
>