Re: [Linux-fbdev-devel] drm_fb_helper: Impossible to change video mode

[Alex Deucher <alexdeucher@gmail.com>]

On Wed, Mar 10, 2010 at 1:47 PM, James Simmons <jsimmons@infradead.org> wrote:
>
>> >> Yuck. See my other post about what fbdev really means in its historical
>> >> context. The struct fb_info really maps better to drm_crtc than to
>> >> drm_framebuffer. In fact take the case of the matrox fbdev driver. It
>> >> creates two framebuffer devices even tho it used one static framebuffer.
>> >> What the driver does is splits the framebuffer in two and assigned each
>> >> part to a CRTC.
>> >
>> > The only problem with that is that it eats a lot of memory for the
>> > console which limits X when it starts. On cards with limited vram ,
>> > you might not have enough memory left for any meaningful acceleration
>> > when X starts.
>>
>> It would be nice to find a way to reclaim the console memory for X,
>> but I'm not sure that can be done and still provide a good way to
>> provide oops support.
>
>        Ah, the power of flags. We had the same issue with user requesting a mode
> change or fbcon asking for a different mode. We handled it with the flag
> FBINFO_MISC_USEREVENT. Since you are using KMS as the backend for fbcon you will
> have to deal also with the ability to change the resolution with tools like stty.
> I can easily see how to do this plus give you more memory like you want :-)
>        For the oops are you talking about printing oops to the screen
> while X is running ? Otherwise if you experience a oops and go back to
> console mode you should be able to view it. The console text buffer is
> independent of the graphics card memory system.
>

Right now we keep the console buffer pinned in vram and we switch to
it when there is an oops or when you switch VTs.

Alex

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