linux-kernel - Re: [PATCH] Revert "drm: Stop resetting connector state to unknown"

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Date:	Tue, 15 Dec 2015 13:23:06 -0500
From:	Rob Clark <robdclark@...il.com>
To:	Lyude <cpaul@...hat.com>
Cc:	David Airlie <airlied@...ux.ie>,
	"open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
	open list <linux-kernel@...r.kernel.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Rui Matos <tiagomatos@...il.com>,
	Julien Wajsberg <felash@...il.com>, kuddel.mail@....de,
	Lennart Poettering <mzxreary@...inter.de>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>
Subject: Re: [PATCH] Revert "drm: Stop resetting connector state to unknown"

On Tue, Dec 15, 2015 at 1:07 PM, Lyude <cpaul@...hat.com> wrote:
> This reverts commit 5677d67ae394 ("drm: Stop resetting connector state to
> unknown")
>
> Unfortunately, not resetting the connector status to unknown actually
> breaks reprobing on suspend/resume in i915, which is important to have
> working since it means a user docking their laptop in suspend won't have
> their monitors work after resume. This commit was originally pushed to fix
> a bug with systemd[1], however said bug has already been fixed in
> userspace.
>
> Since "unknown" is technically a valid option to return to userspace for a
> connector's status, I would think that this sort of behavior should
> probably be expected from userspace. Some good examples of this are the
> radeon driver reporting "unknown" for connectors that have done something
> wonky during a hotplug event (e.g. part of the initialization of the
> connector failed), and the omapdrm driver returns "unknown" for certain
> connector types by default.
>
> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=100641
>
> Signed-off-by: Lyude <cpaul@...hat.com>
> ---
>  drivers/gpu/drm/drm_crtc.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index 24c5434..474e636 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -5312,11 +5312,12 @@ void drm_mode_config_reset(struct drm_device *dev)
>                 if (encoder->funcs->reset)
>                         encoder->funcs->reset(encoder);
>
> -       mutex_lock(&dev->mode_config.mutex);
> -       drm_for_each_connector(connector, dev)
> +       list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
> +               connector->status = connector_status_unknown;
> +
>                 if (connector->funcs->reset)
>                         connector->funcs->reset(connector);
> -       mutex_unlock(&dev->mode_config.mutex);
> +       }
>  }

looks like git-revert might have been a bit over-ambitious and
clobbered a couple subsequent changes.. but that is easy enough to fix
once we figure out what the right thing to do is.

Beyond that.. I'm not really sure how to apply the "do not break
userspace" rule here.. since prior to
c484f02d0f02fbbfc6decc945a69aae011041a27 userspace could see "unknown"
for certain hardware.  But after that commit it could start seeing
"unknown" for drivers/connectors that never would have returned
"unknown" before.  If userspace had a problem with "unknown", it
sounds like a userspace bug that was just unnoticed because no one
tested on the right hardware.

But anyways, one idea to revert things to original behavior prior to
c484f02d0f02fbbfc6decc945a69aae011041a27 (so at least userspace
doesn't see 'unknown' for drivers/connectors that never used to report
'unknown') would be to do something roughly like this in
status_show():

  if (status == unknown)
     status = connector->funcs->detect(connector)

So I could go with either just reverting this commit, or reverting
commit plus above change.  My $0.02 anyways..

BR,
-R

>  EXPORT_SYMBOL(drm_mode_config_reset);
>
> --
> 2.5.0
>
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