From: Kai-Heng Feng <kai.heng.feng@canonical.com>
To: Joerg Roedel <joro@8bytes.org>
Cc: Alex Deucher <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
Date: Thu, 19 Dec 2019 01:45:12 +0800 [thread overview]
Message-ID: <6DC0EAB3-89B5-4A16-9A38-D7AD954DDF1C@canonical.com> (raw)
In-Reply-To: <20191217095341.GG8689@8bytes.org>
> 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:
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
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2019-12-18 17:45 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-29 14:21 [PATCH v2] iommu/amd: Disable IOMMU on Stoney Ridge systems Kai-Heng Feng
2019-12-01 12:42 ` Lucas Stach
2019-12-02 16:36 ` Deucher, Alexander
2019-12-04 16:08 ` Deucher, Alexander
2019-12-06 5:59 ` Kai-Heng Feng
2019-12-06 8:57 ` Christian König
2019-12-02 17:00 ` Christoph Hellwig
2019-12-06 5:57 ` Kai-Heng Feng
2019-12-17 9:53 ` Joerg Roedel
2019-12-18 17:45 ` Kai-Heng Feng [this message]
2019-12-19 19:15 ` Deucher, Alexander
2019-12-20 2:13 ` Kai-Heng Feng
2020-01-06 8:37 ` Kai-Heng Feng
2020-02-05 10:10 ` Kai-Heng Feng
2020-02-05 13:24 ` Joerg Roedel
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=6DC0EAB3-89B5-4A16-9A38-D7AD954DDF1C@canonical.com \
--to=kai.heng.feng@canonical.com \
--cc=alexander.deucher@amd.com \
--cc=iommu@lists.linux-foundation.org \
--cc=joro@8bytes.org \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).