Re: [RFC PATCH] drm/ssd130x: Allocate buffer in the CRTC's .atomic_check() callback
From: Thomas Zimmermann
Date: Fri Sep 01 2023 - 06:59:15 EST
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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