Re: [PATCH] drm/i915/display: use IS_ERR_OR_NULL macro on DP tunnel mgr creation failure

[Michal Wajdeczko <michal.wajdeczko@intel.com>]

On 11.12.2024 10:56, Krzysztof Karas wrote:
> drm_dp_tunnel_mgr_create() may return NULL on failure, which will not
> be caught via IS_ERR(), so replace it with IS_ERR_OR_NULL() macro.
> 
> Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_tunnel.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_tunnel.c b/drivers/gpu/drm/i915/display/intel_dp_tunnel.c
> index 94198bc04939..6c960416f776 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_tunnel.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_tunnel.c
> @@ -793,7 +793,7 @@ int intel_dp_tunnel_mgr_init(struct intel_display *display)
>  	drm_connector_list_iter_end(&connector_list_iter);
>  
>  	tunnel_mgr = drm_dp_tunnel_mgr_create(display->drm, dp_connectors);
> -	if (IS_ERR(tunnel_mgr))
> +	if (IS_ERR_OR_NULL(tunnel_mgr))
>  		return PTR_ERR(tunnel_mgr);

this still will not work as expected, since in case of NULL it will
return 0 (success) instead of "a negative error code" as described in
the documentation of the intel_dp_tunnel_mgr_init()

OTOH the documentation of drm_dp_tunnel_mgr_create() says: "Returns a
pointer to the tunnel manager if created successfully or NULL in case of
an error" so more appropriate fix seems to be:

-	if (IS_ERR(tunnel_mgr))
- 		return PTR_ERR(tunnel_mgr);
+	if (!tunnel_mgr)
+ 		return -ENOMEM;

but then it will not work with the drm_dp_tunnel_mgr_create() stub which
actually returns undocumented ERR_PTR(-EOPNOTSUPP)

so unless you are ready to update implementation and documentation of
the drm_dp_tunnel_mgr_create() to return ERR_PTR instead of NULL in case
of error, the fix IMO should look more like:

+	if (!tunnel_mgr)
+ 		return -ENOMEM;

and keep existing IS_ERR check

>  
>  	display->dp_tunnel_mgr = tunnel_mgr;