linux-kernel - Re: [PATCH v1] drm/modes: Skip invalid cmdline mode

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Date:   Fri, 12 Jul 2019 10:10:27 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <sean@...rly.run>, Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] drm/modes: Skip invalid cmdline mode

On Thu, Jul 11, 2019 at 06:55:03PM +0300, Dmitry Osipenko wrote:
> 11.07.2019 12:03, Maxime Ripard пишет:
> > On Wed, Jul 10, 2019 at 06:05:18PM +0300, Dmitry Osipenko wrote:
> >> 10.07.2019 17:05, Maxime Ripard пишет:
> >>> On Wed, Jul 10, 2019 at 04:29:19PM +0300, Dmitry Osipenko wrote:
> >>>> This works:
> >>>>
> >>>> diff --git a/drivers/gpu/drm/drm_client_modeset.c b/drivers/gpu/drm/drm_client_modeset.c
> >>>> index 56d36779d213..e5a2f9c8f404 100644
> >>>> --- a/drivers/gpu/drm/drm_client_modeset.c
> >>>> +++ b/drivers/gpu/drm/drm_client_modeset.c
> >>>> @@ -182,6 +182,8 @@ drm_connector_pick_cmdline_mode(struct drm_connector *connector)
> >>>>         mode = drm_mode_create_from_cmdline_mode(connector->dev, cmdline_mode);
> >>>>         if (mode)
> >>>>                 list_add(&mode->head, &connector->modes);
> >>>> +       else
> >>>> +               cmdline_mode->specified = false;
> >>>
> >>> Hmmm, it's not clear to me why that wouldn't be the case.
> >>>
> >>> If we come back to the beginning of that function, we retrieve the
> >>> cmdline_mode buffer from the connector pointer, that will probably
> >>> have been parsed a first time using drm_mode_create_from_cmdline_mode
> >>> in drm_helper_probe_add_cmdline_mode.
> >>>
> >>> Now, I'm guessing that the issue is that in
> >>> drm_mode_parse_command_line_for_connector, if we have a named mode, we
> >>> just copy the mode over and set mode->specified.
> >>>
> >>> And we then move over to do other checks, and that's probably what
> >>> fails and returns, but our drm_cmdline_mode will have been modified.
> >>>
> >>> I'm not entirely sure how to deal with that though.
> >>>
> >>> I guess we could allocate a drm_cmdline_mode structure on the stack,
> >>> fill that, and if successful copy over its content to the one in
> >>> drm_connector. That would allow us to only change the content on
> >>> success, which is what I would expect from such a function?
> >>>
> >>> How does that sound?
> >>
> >> I now see that there is DRM_MODE_TYPE_USERDEF flag that is assigned only
> >> for the "cmdline" mode and drm_client_rotation() is the only place in
> >> DRM code that cares about whether mode is from cmdline, hence looks like
> >> it will be more correct to do the following:
> >
> > I'm still under the impression that we're dealing with workarounds of
> > a more central issue, which is that we shouldn't return a partially
> > modified drm_cmdline_mode.
> >
> > You said it yourself, the breakage is in the commit changing the
> > command line parsing logic, while you're fixing here some code that
> > was introduced later on.
>
> The problem stems from assumption that *any* named mode is valid. It
> looks to me that the ultimate solution would be to move the mode's name
> comparison into the [1], if that's possible.
>
> [1] drm_mode_parse_command_line_for_connector()

Well, one could argue that video=tegrafb is invalid and should be
rejected as well, but we haven't cleared that up.

> > Can you try the followintg patch?
> > http://code.bulix.org/8cwk4c-794565?raw
>
> This doesn't help because the problem with the rotation_reflection is
> that it's 0 if "rotation" not present in the cmdline and then ilog2(0)
> returns -1. So the patch "drm/modes: Don't apply cmdline's rotation if
> it wasn't specified" should be correct in any case.

So we would have the same issue with rotate=0 then?

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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