Re: drm/ssd130x: stale pixels when the GPU renders into the framebuffer

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 30.09.26 um 20:45 schrieb Fabio Piparo:
> Hi all,
>
> On Wed, Sep 30, 2026 at 2:48 AM Thomas Zimmermann wrote:
>> Those buffers should have been allocated on the v3d side.
> Ah! Now I think I see what's happening. Some context on where I'm
> coming from, since I think I explained it badly.
>
> My program opens the panel's card and lets Mesa handle the buffers.
>
>      fd   = open("/dev/dri/card2", O_RDWR);        /* ssd130x */
>      gbm  = gbm_create_device(fd);
>      surf = gbm_surface_create(gbm, 128, 32, GBM_FORMAT_XRGB8888,
>                                GBM_BO_USE_SCANOUT | GBM_BO_USE_RENDERING);
>      bo = gbm_surface_lock_front_buffer(surf);
>
> On a Pi 4/5 Mesa hands me dumb buffers from ssd130x with v3d drawing
> into them. On a Pi 0-3 it goes the other way, the GPU makes the
> buffers and ssd130x imports them, and that works fine.
>
> Reading this thread convinced me that what I was doing was wrong for
> my use case, and that my program should own the buffers itself. So now
> it does the producer-consumer thing:
>
>      gpu = gbm_create_device(open("/dev/dri/renderD128", O_RDWR)); /* v3d */
>      bo  = gbm_bo_create(gpu, 128, 32, GBM_FORMAT_XRGB8888,
>                          GBM_BO_USE_RENDERING | GBM_BO_USE_LINEAR);
>      drmPrimeFDToHandle(fd, gbm_bo_get_fd(bo), &handle);
>      /* AddFB2 with that handle, draw into bo through an EGLImage, page flip */
>
> That's clean on a stock kernel and stock Mesa.

Great to hear that it works now

Best regards
Thomas

>
> By the way, I found one other report that looks like the same thing,
> from March 2024: https://github.com/notro/gud/issues/22
>
> Thanks,
> Fabio/

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)