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Subject: Re: [PATCH v1] drm/modes: Skip invalid cmdline mode
From:   Dmitry Osipenko <digetx@gmail.com>
To:     Maxime Ripard <maxime.ripard@bootlin.com>
Cc:     Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Sean Paul <sean@poorly.run>, Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@linux.ie>,
        dri-devel@lists.freedesktop.org, linux-tegra@vger.kernel.org,
        linux-kernel@vger.kernel.org
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Date:   Wed, 10 Jul 2019 18:45:47 +0300
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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.