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

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Date:   Wed, 10 Jul 2019 16:05:04 +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 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?

Maxime

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

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