linux-kernel - Re: [PATCH] drm/vc4: Allow using more than 256MB of CMA memory.

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Date:   Fri, 14 Apr 2017 11:07:20 -0700
From:   Eric Anholt <eric@...olt.net>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/vc4: Allow using more than 256MB of CMA memory.

Boris Brezillon <boris.brezillon@...e-electrons.com> writes:

> On Mon, 27 Mar 2017 16:10:25 -0700
> Eric Anholt <eric@...olt.net> wrote:
>
>> Until now, we've had to limit Raspberry Pi to 256MB of CMA memory to
>> keep from triggering the hardware addressing bug between of the tile
>> binner of the tile alloc memory (where the top 4 bits come from the
>> tile state data array's address).
>> 
>> To work around that and allow more memory to be reserved for graphics,
>> allocate a single BO to store tile state data arrays and tile
>> alloc/overflow memory while the GPU is active, and make sure that that
>> one BO doesn't happen to cross a 256MB boundary.  With that in place,
>> we can allocate textures and shaders anywhere in system memory (still
>> contiguous, of course).
>
> It's hard to review something I don't quite understand, but I didn't
> spot any problem and the code seems to follow what the commit message
> says: make sure the memory used by the tile binner (still have to look
> at what a tile binner is :-)) does not cross a 256MB.
>
> So, not sure my review has a real value here, but
>
> Reviewed-by: Boris Brezillon <boris.brezillon@...e-electrons.com>

It's still more review than vc4 patches used to get, so I'm happy.
Thanks!

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