[RFC][PATCH 1/2] drm: Improve PATH prop docs

[Pekka Paalanen]

On Thu, 13 Jun 2019 21:43:34 +0300
Ville Syrjala <ville.syrjala at linux.intel.com> wrote:

> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> The PATH blob is already being parsed by userspace for MST connectors
> so the layout of the blob is now uabi. Let's document what it should
> look like.
> 
> Also add a clear note saying non-MST connectors can have a PATH prop
> too.
> 
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Pekka Paalanen <ppaalanen at gmail.com>
> Cc: Ilia Mirkin <imirkin at alum.mit.edu>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/drm_connector.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index e17586aaa80f..ce3926e9ad11 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -899,7 +899,16 @@ static const struct drm_prop_enum_list hdmi_colorspaces[] = {
>   * 	connected. Used by DP MST. This should be set by calling
>   * 	drm_connector_set_path_property(), in the case of DP MST with the
>   * 	path property the MST manager created. Userspace cannot change this
> - * 	property.
> + * 	property. The value must be an ASCII string.
> + *
> + * 	For DP MST connectors the path string follows the pattern
> + * 	"mst:<base connector ID>[-<mst port>]...", where the base connector ID
> + * 	identifies the DP connector on the source device, and the mst ports
> + * 	are the port numbers in the DP MST topology.

Hi,

what exactly is the connector ID as already used here for MST? Is it
not persistent?

I assume the MST port numbers are persistent as long as the physical
topology does not change.

> + *
> + * 	For non-DP MST connectors the format is freeform, as long as it
> + * 	uniquely identifies the physical path, remains stable across
> + * 	kernel releases, and does not start with "mst:".

Maybe the requirements for "persistent name" should be clarified more:
- remains stable across kernel releases
- is immune to driver loading/initialisation order changes
- is immune to adding or removing other hardware (e.g. graphics cards)

Maybe also some explicit words about what to do with dynamic non-MST
connectors?


Thanks,
pq
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