Re: [PATCH v2] drm: document that user-space should force-probe connectors

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Mon, 30 Nov 2020 16:26:12 +0000
Simon Ser <contact@emersion.fr> wrote:

> It seems like we can't have nice things, so let's just document the
> disappointing behaviour instead.
> 
> The previous version assumed the kernel would perform the probing work
> when appropriate, however this is not the case today. Update the
> documentation to reflect reality.

Hi Simon,

yeah, this message actually explains something. Good.

> v2:
> 
> - Improve commit message to explain why this change is made (Pekka)
> - Keep the bit about flickering (Daniel)
> - Explain when user-space should force-probe, and when it shouldn't (Daniel)
> 
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Fixes: 2ac5ef3b2362 ("drm: document drm_mode_get_connector")
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Pekka Paalanen <ppaalanen@gmail.com>
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> ---
>  include/uapi/drm/drm_mode.h | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index b49fbf2bdc40..1c064627e6c3 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -414,15 +414,12 @@ enum drm_mode_subconnector {
>   *
>   * If the @count_modes field is set to zero, the kernel will perform a forced
>   * probe on the connector to refresh the connector status, modes and EDID.
> - * A forced-probe can be slow and the ioctl will block. A force-probe can cause
> - * flickering and temporary freezes, so it should not be performed
> - * automatically.
> + * A forced-probe can be slow, might cause flickering and the ioctl will block.
>   *
> - * User-space shouldn't need to force-probe connectors in general: the kernel
> - * will automatically take care of probing connectors that don't support
> - * hot-plug detection when appropriate. However, user-space may force-probe
> - * connectors on user request (e.g. clicking a "Scan connectors" button, or
> - * opening a UI to manage screens).
> + * User-space needs to force-probe connectors to ensure their metadata is
> + * up-to-date at startup and after receiving a hot-plug event. User-space
> + * may perform a forced-probe when the user explicitly requests it. User-space
> + * shouldn't perform a forced-probe in other situations.
>   */
>  struct drm_mode_get_connector {
>  	/** @encoders_ptr: Pointer to ``__u32`` array of object IDs. */

Sounds good, err... accurate to me.

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.com>


Thanks,
pq

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