Re: [PATCH] fbdev: Remove udlfb driver

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 01.12.20 um 12:20 schrieb Mikulas Patocka:
> 
> 
> On Tue, 1 Dec 2020, Thomas Zimmermann wrote:
> 
>> Hi
>>
>> Am 30.11.20 um 19:39 schrieb Mikulas Patocka:
>>>
>>>
>>> On Mon, 30 Nov 2020, Daniel Vetter wrote:
>>>
>>>> On Mon, Nov 30, 2020 at 09:31:15AM -0500, Mikulas Patocka wrote:
>>>>>
>>>>> The framebuffer driver supports programs running full-screen directly on
>>>>> the framebuffer console, such as web browser "links -g", image viewer
>>>>> "fbi", postscript+pdf viewer "fbgs", ZX Spectrum emulator "fuse-sdl",
>>>>> movie player "mplayer -vo fbdev". The DRM driver doesn't run them.
>>>>
>>>> Hm this should in general work on drm drivers. Without that it's clear the
>>>> switch-over isn't really ready yet.
>>>
>>> I fixed it with this patch two years ago:
>>> https://lists.freedesktop.org/archives/dri-devel/2018-June/179023.html
>>>
>>> But the patch never went through and the fb_defio feature was removed in
>>> the kernel 5.6 (commit d0c4fc5a4814e431c15272935c8dc973c18073aa).
>>>
>>>
>>> Without fb_defio, the only other possibility how to update the screen is
>>> the ioctl DRM_IOCTL_MODE_DIRTYFB. But this ioctl requires master mode, so
>>> user programs like "links -g" can't issue it.
>>
>> That's confusing. DIRTYFB is only for DRM.
> 
> Yes, you're right.
> 
>> And why can links not run as DRM master mode? If it renders to the terminal,
>> it should act like a composer. In that case it almost certainly wants master
>> status.
>>
>> Best regards
>> Thomas
> 
> How can a userspace program acquire master mode without being suid?

For my understanding, there's no easy solution to that. :/

I guess we (DRM devs) have to treat fbdev as the solution for use cases 
such as ours.

For the unplug issue, I'll try to reproduce and fix it.

For the performance problems, we might be able to squeeze a few more 
cycles out of it.

Best regards
Thomas

> 
> Is there some "Hello World!" program that shows how to use DRM? I'm not an
> expert in DRM, but if there were some tutorial+documentation, I could
> consider porting "links" to it.
> 
> Mikulas
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer


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