Messages in this thread | | | Date | Thu, 2 Apr 2015 18:06:34 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86, aperture: Check for GART before accessing GART registers |
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* Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com> wrote:
> On 4/2/2015 5:01 AM, Ingo Molnar wrote: > >* Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com> 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. > >In what fashion did this problem manifest itself on real systems? > > > > > > This code doesn't break on existing processors. > There are some other side effects though.. > > We get "AGP:" messages on kernel logs like this- > [ 0.000000] AGP: Node 0: aperture [bus addr 0x00000000-0x01ffffff] (32MB) > [ 0.000000] AGP: Your BIOS doesn't leave a aperture memory hole > [ 0.000000] AGP: Please enable the IOMMU option in the BIOS setup > [ 0.000000] AGP: This costs you 64MB of RAM > [ 0.000000] AGP: Mapping aperture over RAM [mem 0xd4000000-0xd7ffffff] > (65536KB) > > These are just noise on processors which have no GART.
agreed.
> We can avoid calling allocate_aperture() and would not have to > memblock_reserve() 64MB of RAM. > Also, we can avoid having to loop through all PCI buses, devices (twice) > searching for AGP bridge if we bail out early.
Makes sense. Mind adding this info to the changelog and resend?
Thanks,
Ingo
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