Message-ID: <51C69732.1010906@gmail.com>
Date: Sun, 23 Jun 2013 08:35:30 +0200
From: Brice Goglin <brice.goglin@gmail.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130518 Icedove/17.0.5
MIME-Version: 1.0
To: "H. Peter Anvin" <hpa@zytor.com>
CC: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        David Airlie <airlied@linux.ie>, dri-devel@lists.freedesktop.org
Subject: Re: MTRR use in drivers
References: <51C3DDFA.7050204@zytor.com>
In-Reply-To: <51C3DDFA.7050204@zytor.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1118
Lines: 29

Le 21/06/2013 07:00, H. Peter Anvin a ?crit :
> An awful lot of drivers, mostly DRI drivers, are still mucking with
> MTRRs directly as opposed to using ioremap_wc() or similar interfaces.
> In addition to the architecture dependency, this is really undesirable
> because MTRRs are a limited resource, whereas page table attributes are not.
>
> Furthermore, this perpetuates the need for the horrific hack known as
> "MTRR cleanup".
>
> What, if anything, can we do to clean up this mess?
>
> 	-hpa
>

The first network driver that used ioremap_wc() back in 2008 (myri10ge)
had to keep using MTRR because ioremap_wc() silently falls back to
ioremap_nocache() when PAT is disabled.

I asked about this in https://lkml.org/lkml/2008/5/31/42 and there was
some talk about putting the MTRR addition in the nocache fallback path
but I guess nobody implemented the idea.

Brice

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/