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

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Date:   Wed, 10 Jul 2019 19:03:03 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Maxime Ripard <maxime.ripard@...tlin.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

10.07.2019 18:45, Dmitry Osipenko пишет:
> 10.07.2019 18:05, Dmitry Osipenko пишет:
>> 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:
>>
>> diff --git a/drivers/gpu/drm/drm_client_modeset.c
>> b/drivers/gpu/drm/drm_client_modeset.c
>> index 56d36779d213..e5b3be9ed689 100644
>> --- a/drivers/gpu/drm/drm_client_modeset.c
>> +++ b/drivers/gpu/drm/drm_client_modeset.c
>> @@ -825,6 +825,7 @@ bool drm_client_rotation(struct drm_mode_set
>> *modeset, unsigned int *rotation)
>>  {
>>         struct drm_connector *connector = modeset->connectors[0];
>>         struct drm_plane *plane = modeset->crtc->primary;
>> +       struct drm_display_mode *mode = modeset->mode;
>>         struct drm_cmdline_mode *cmdline;
>>         u64 valid_mask = 0;
>>         unsigned int i;
>> @@ -859,7 +860,7 @@ bool drm_client_rotation(struct drm_mode_set
>> *modeset, unsigned int *rotation)
>>          * simple XOR between the two handle the addition nicely.
>>          */
>>         cmdline = &connector->cmdline_mode;
>> -       if (cmdline->specified) {
>> +       if (mode->flags & DRM_MODE_TYPE_USERDEF) {
>>                 unsigned int cmdline_rest, panel_rest;
>>                 unsigned int cmdline_rot, panel_rot;
>>                 unsigned int sum_rot, sum_rest;
>>
> 
> Although, then rotation won't be applied to the named mode in that case.
> 
> Seems the fix could be even simpler:
> 
> @@ -859,7 +859,7 @@ bool drm_client_rotation(struct drm_mode_set
> *modeset, unsigned int *rotation)
>          * simple XOR between the two handle the addition nicely.
>          */
>         cmdline = &connector->cmdline_mode;
> -       if (cmdline->specified) {
> +       if (cmdline->specified && cmdline->rotation_reflection) {
>                 unsigned int cmdline_rest, panel_rest;
>                 unsigned int cmdline_rot, panel_rot;
>                 unsigned int sum_rot, sum_rest;
> 
> And looks like there is another problem here.. the cmdline's rotation
> overrides *all* modes while the doc/fb/modedb.rst claims that rotation
> is applied only to the *initial* mode.
> 

Actually, I was wrong here. This rotation is getting applied only to the
framebuffer's console, so looks fine.

I guess it's also okay to just keep applying cmdline's rotation even if
the mode is invalid. Please let me know if you have any objections.