linux-kernel - Re: [PATCH V2] x86/gart: Check for GART support before accessing GART registers

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Message-ID: <20150408152522.GH3611@pd.tnic>
Date:	Wed, 8 Apr 2015 17:25:22 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>
Cc:	mingo@...hat.com, bp@...e.de, linux-kernel@...r.kernel.org,
	Suravee.Suthikulpanit@....com, Joerg Rodel <joro@...tes.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, x86-ml <x86@...nel.org>
Subject: Re: [PATCH V2] x86/gart: Check for GART support before accessing
 GART registers

On Tue, Apr 07, 2015 at 04:46:37PM -0500, Aravind Gopalakrishnan wrote:
> GART registers are not present in newer processors (Fam15h, Model 10h
> and later). So, avoid accesses to GART registers in PCI config
> space by returning early in early_gart_iommu_check() and
> gart_iommu_hole_init() if GART is not available.
> 
> Current code doesn't break on existing processors but there are some
> side effects:
> 
> We get bogus AGP aperture messages which are simply noise on
> GART-less processors:
> 
>   AGP: Node 0: aperture [bus addr 0x00000000-0x01ffffff] (32MB)
>   AGP: Your BIOS doesn't leave aperture memory hole
>   AGP: Please enable the IOMMU option in the BIOS setup
>   AGP: This costs you 64MB of RAM
>   AGP: Mapping aperture over RAM [mem 0xd4000000-0xd7ffffff]
> 
> We can avoid calling allocate_aperture() and would not have to
> wastefully reserve 64MB of RAM with memblock_reserve(). Also, we can
> avoid having to loop through all PCI buses and devices twice, searching
> for a non-existent AGP bridge if we bail out early.
> 
> Refactoring the family check used in amd_nb.c into an inline function
> so we can use it here as well as in amd_nb.c
> 
> Fix some typos while at it.
> Tested the patch on Fam10h and Fam15h Model 00h-fh and this code
> runs fine. On Fam15h Model 60h-6fh and on Fam16h, we bail early
> as they don't have GART.
> 
> Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>
> Reviewed-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> Cc: Joerg Rodel <joro@...tes.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: x86-ml <x86@...nel.org>
> ---
> Changes in V2:
>  - move amd_gart_present() before any other checks as it's least intrusive (per Boris)
>  - fix typos in code and commit message (per Ingo)
>  - minor change to subject line (per Boris' change)
>  - Link to V1:http://marc.info/?l=linux-kernel&m=142792069809730&w=2
> 
>  arch/x86/include/asm/amd_nb.h | 11 +++++++++++
>  arch/x86/kernel/amd_nb.c      |  4 +---
>  arch/x86/kernel/aperture_64.c |  8 +++++++-
>  3 files changed, 19 insertions(+), 4 deletions(-)

Applied, thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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