Hi Am 06.03.23 um 23:19 schrieb Linus Walleij:
On Wed, Mar 1, 2023 at 4:31 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:Add fbdev emulation that is optimized for DMA helpers, as used by most drivers. It operates directly on GEM DMA buffers in system memory. Memory pages are mmap'ed directly to userspace. No implicit shadow buffers need to be allocated; as can happen with the generic fbdev emulation. Convert drivers that fulfil the requirements. Tested with fbcon and IGT on vc4. Future direction: providing a dedicated fbdev emulation for GEM DMA helpers will allow us to remove this case from the generic fbdev code. The latter can then be simplified.1) I love your work.
Thank you. :)
2) Why isn't this DRM driver changed? drivers/gpu/drm/mcde/mcde_drv.c AFAICT it also uses GEM buffers in system memory.
This driver requires damage handling https://elixir.bootlin.com/linux/v6.2/source/drivers/gpu/drm/mcde/mcde_drv.c#L97 for which we have to call the framebuffer's dirty callback https://elixir.bootlin.com/linux/v6.2/source/drivers/gpu/drm/drm_gem_framebuffer_helper.c#L285 after each write.Doing this with fbdev emulation requires tracking of mmap'ed pages via fbdev's deferred-I/O mechanisms. That makes the fbdev-emulation code more complex. AFAICT, the existing generic fbdev emulation already implements this case 'good enough.'
3) This one: drivers/gpu/drm/pl111/pl111_drv.c is also very similar, but can sometimes use a dedicated RAM memory for allocations using CMA, does that make it not a candidate?
Thanks, I think I simply missed pl111. Best regards Thomas
They aren't much different in how they work from the TVE200. Yours, Linus Walleij
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev
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