linux-kernel - Re: MTRR use in drivers

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Message-ID: <51C75CD6.5010206@zytor.com>
Date:	Sun, 23 Jun 2013 13:38:46 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Dave Airlie <airlied@...il.com>
CC:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Brice Goglin <brice.goglin@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: MTRR use in drivers

On 06/23/2013 01:30 PM, Dave Airlie wrote:
>>>> Why do you care about performance when PAT is disabled?
> 
> breaking old boxes just because, is just going to get reverted when I
> get the first regression report that you broke old boxes.
> 

Not "just because", but *if* the choice is between breaking old boxes
and breaking new boxes I'll take the latter.

> Andy Lutomirski just submitted a bunch of patches to clean up the DRM
> usage of mtrrs, they are in drm-next, afaik we no longer add them on
> PAT systems.

Fantastic news.  No issue, then, and no need to break anything.

The only problem I see with having ioremap_wc() installing an MTRR on
non-PAT, rather than pushing that into the drivers which is clearly not
the right thing, is that we will need a hook to uninstall it when the
mapping is destroyed.

	-hpa



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