Messages in this thread | | | Subject | Re: [PATCH v2] iommu/amd: Disable IOMMU on Stoney Ridge systems | From | Kai-Heng Feng <> | Date | Wed, 5 Feb 2020 18:10:11 +0800 |
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Hi Joerg,
> On Jan 6, 2020, at 16:37, Kai-Heng Feng <kai.heng.feng@canonical.com> wrote: > > > >> On Dec 20, 2019, at 10:13, Kai-Heng Feng <kai.heng.feng@canonical.com> wrote: >> >> >> >>> 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. > > Any further suggestion to let me try?
Since using identity mapping with ATS doesn't help, Is it possible to merge this patch as is?
Kai-Heng
> > Kai-Heng > >> >> 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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