Re: [PATCH] drm/etnaviv: move GPU linear window to end of DMA window - Russell King

From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Lucas Stach <l.stach@pengutronix.de>
Cc: dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/etnaviv: move GPU linear window to end of DMA window
Date: Wed, 9 Mar 2016 12:25:08 +0000	[thread overview]
Message-ID: <20160309122507.GP19428@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <1456762816-496-1-git-send-email-l.stach@pengutronix.de>

On Mon, Feb 29, 2016 at 05:20:16PM +0100, Lucas Stach wrote:
> If the end of the system DMA window is farther away from the start of
> physical RAM than the size of the GPU linear window, move the linear
> window so that it ends at the same address than the system DMA window.
> 
> This allows to map command buffer from CMA, which is likely to reside
> at the end of the system DMA window, while also overlapping as much
> RAM as possible, in order to optimize regular buffer mappings through
> the linear window.

I've been pondering this for a while now, and I think we should not
do this unconditionally - it should be predicated on the MC20 feature -
both for the original code and the new code.  If we don't have the MC20
feature, we end up with more memory spaces than we can cope with.

If we don't have MC20, but we need to offset, that's an error which
can lead to memory corruption.

-- 
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