linux-kernel - Re: [RFC PATCH] drm/ssd130x: Allocate buffer in the CRTC's .atomic

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Message-ID: <5dj43wxsszikpwbwzxx5v5h7jbx4vjjavnhzi26xgfcdp5wsws@t2hd3pawau4t>
Date:   Fri, 1 Sep 2023 10:25:02 +0200
From:   Maxime Ripard <mripard@...nel.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [RFC PATCH] drm/ssd130x: Allocate buffer in the CRTC's
 .atomic_check() callback

On Fri, Sep 01, 2023 at 09:48:09AM +0200, Javier Martinez Canillas wrote:
> Thomas Zimmermann <tzimmermann@...e.de> 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:
> Allocate buffer in the plane's .atomic_check() callback") but just make
> them fixed arrays with the size of the biggest format.
> 
> 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.

If we want to go that road, we don't even need an extra allocation, it
can be part of the state or object structure itself.

Maxime

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