Messages in this thread | | | Subject | Re: [PATCH v2] iommu/amd: Disable IOMMU on Stoney Ridge systems | From | Kai-Heng Feng <> | Date | Fri, 20 Dec 2019 10:13:58 +0800 |
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> On Dec 20, 2019, at 03:15, Deucher, Alexander <Alexander.Deucher@amd.com> wrote: > >> -----Original Message----- >> From: Kai-Heng Feng <kai.heng.feng@canonical.com> >> Sent: Wednesday, December 18, 2019 12:45 PM >> To: Joerg Roedel <joro@8bytes.org> >> Cc: Christoph Hellwig <hch@infradead.org>; Deucher, Alexander >> <Alexander.Deucher@amd.com>; iommu@lists.linux-foundation.org; Kernel >> development list <linux-kernel@vger.kernel.org> >> Subject: Re: [PATCH v2] iommu/amd: Disable IOMMU on Stoney Ridge >> systems >> >> >> >>> On Dec 17, 2019, at 17:53, Joerg Roedel <joro@8bytes.org> wrote: >>> >>> On Fri, Dec 06, 2019 at 01:57:41PM +0800, Kai-Heng Feng wrote: >>>> Hi Joerg, >>>> >>>>> On Dec 3, 2019, at 01:00, Christoph Hellwig <hch@infradead.org> wrote: >>>>> >>>>> On Fri, Nov 29, 2019 at 10:21:54PM +0800, Kai-Heng Feng wrote: >>>>>> Serious screen flickering when Stoney Ridge outputs to a 4K monitor. >>>>>> >>>>>> According to Alex Deucher, IOMMU isn't enabled on Windows, so let's >>>>>> do the same here to avoid screen flickering on 4K monitor. >>>>> >>>>> Disabling the IOMMU entirely seem pretty severe. Isn't it enough to >>>>> identity map the GPU device? >>>> >>>> Ok, there's set_device_exclusion_range() to exclude the device from >> IOMMU. >>>> However I don't know how to generate range_start and range_length, >> which are read from ACPI. >>> >>> set_device_exclusion_range() is not the solution here. The best is if >>> the GPU device is put into a passthrough domain at boot, in which it >>> will be identity mapped. DMA still goes through the IOMMU in this >>> case, but it only needs to lookup the device-table, page-table walks >>> will not be done anymore. >>> >>> The best way to implement this is to put it into the >>> amd_iommu_add_device() in drivers/iommu/amd_iommu.c. There is this >>> check: >>> >>> if (dev_data->iommu_v2) >>> iommu_request_dm_for_dev(dev); >>> >>> The iommu_request_dm_for_dev() function causes the device to be >>> identity mapped. The check can be extended to also check for a device >>> white-list for devices that need identity mapping. >> >> My patch looks like this but the original behavior (4K screen flickering) is still >> the same: > > Does reverting the patch to disable ATS along with this patch help?
Unfortunately it doesn't help.
Kai-Heng
> > Alex > >> >> diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c >> index bd25674ee4db..f913a25c9e92 100644 >> --- a/drivers/iommu/amd_iommu.c >> +++ b/drivers/iommu/amd_iommu.c >> @@ -42,6 +42,7 @@ >> #include <asm/iommu.h> >> #include <asm/gart.h> >> #include <asm/dma.h> >> +#include <asm/pci-direct.h> >> >> #include "amd_iommu_proto.h" >> #include "amd_iommu_types.h" >> @@ -2159,6 +2160,8 @@ static int amd_iommu_add_device(struct device >> *dev) >> struct iommu_domain *domain; >> struct amd_iommu *iommu; >> int ret, devid; >> + bool need_identity_mapping = false; >> + u32 header; >> >> if (!check_device(dev) || get_dev_data(dev)) >> return 0; >> @@ -2184,7 +2187,11 @@ static int amd_iommu_add_device(struct device >> *dev) >> >> BUG_ON(!dev_data); >> >> - if (dev_data->iommu_v2) >> + header = read_pci_config(0, PCI_BUS_NUM(devid), PCI_SLOT(devid), >> PCI_FUNC(devid)); >> + if ((header & 0xffff) == 0x1002 && (header >> 16) == 0x98e4) >> + need_identity_mapping = true; >> + >> + if (dev_data->iommu_v2 || need_identity_mapping) >> iommu_request_dm_for_dev(dev); >> >> /* Domains are initialized for this device - have a look what we ended up >> with */ >> >> >> $ dmesg | grep -i direct >> [ 0.011446] Using GB pages for direct mapping >> [ 0.703369] pci 0000:00:01.0: Using iommu direct mapping >> [ 0.703830] pci 0000:00:08.0: Using iommu direct mapping >> >> So the graphics device (pci 0000:00:01.0:) is using direct mapping after the >> change. >> >> Kai-Heng >> >>> >>> HTH, >>> >>> Joerg
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