Hi Am 01.09.23 um 09:48 schrieb Javier Martinez Canillas:
Thomas Zimmermann <tzimmermann@xxxxxxx> writes:Hi Javier, another idea about this patch: why not just keep the allocation in the plane's atomic check, but store the temporary buffers in a plane struct. You'd only grow the arrays length in atomic_check and later fetch the pointers in atomic_update. It needs some locking, but nothing complicated.Yes, that would work too. Another option is to just move the buffers to struct ssd130x_device as it was before commit 45b58669e532 ("drm/ssd130x:
Adding something like a struct ssd130x_plane that holds the temporary memory has the advantage of making a clear connection between the memory and the plane. If nothing else, to the next programmer reading the code.
Allocate buffer in the plane's .atomic_check() callback") but just make them fixed arrays with the size of the biggest format.
What is the size of the biggest format? I haven't read the driver code, but a shadow plane can be up to 4096 pixels wide. It's 16 KiB for XRGB888. Not too much, but not nothing either.
To reduce allocation and/or locking overhead, you could try to update the pointers in the plane struct with RCU semantics. Plane updates would use whatever pointer they saw, while the plane's atomic_check could grow the memory buffers as necessary.
Best regards Thomas
That will be some memory wasted but will prevent the problem of trying to allocate buffers after drm_atomic_helper_swap_state() has been called.Best regards Thomas Am 30.08.23 um 08:25 schrieb Javier Martinez Canillas:
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)
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