* Stephen Warren wrote: > On 05/21/2012 11:05 AM, Lucas Stach wrote: > > Am Montag, den 21.05.2012, 10:41 -0600 schrieb Stephen Warren: > >> On 05/21/2012 08:11 AM, Thierry Reding wrote: > >>> * Hiroshi DOYU wrote: > >>>> GART Register/Aperture range should be reserved. > >> ... > >>>> diff --git a/drivers/iommu/tegra-gart.c > >>>> b/drivers/iommu/tegra-gart.c > >> ... > >>>> + if (!devm_request_mem_region(dev, res_remap->start, + > >>>> resource_size(res_remap), dev_name(dev))) { + dev_err(dev, > >>>> "failed to reserve GART aperture\n"); + return -EBUSY; + } + > >>> > >>> I'm not so sure that this is a good idea. If the GART driver > >>> requests the GART aperture, then users of the GART aperture (e.g. > >>> the DRM driver) will no longer be able to use it. > >> > >> Presumably the DRM driver would be obtaining access to parts of the > >> GART aperture through the GART driver, rather than just grabbing the > >> IO region and using it for itself? > > > > With a TTM-like memory manager the DRM driver will take over the address > > space management of the GART aperture. The GART driver is only used to > > set up the mappings in the IOMMU. The DRM driver is the one that sets > > up/tears down the CPU mappings on demand, so the aperture should be > > claimed in the DRM driver. > > Even if the DRM driver is managing the aperture, I still think the GART > driver should claim it. The physical address of the aperture is a > property of the GART, so only the GART's resources (and DT node) should > contain a representation of where that aperture is. The DRM driver > should call into the GART driver to find out where the aperture is, and > hence GART is able to claim it without conflict. That could be difficult to do. There isn't any API to allow this. I guess if something like that is added it should probably go into the IOMMU framework. Thierry
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