On Fri, Sep 02, 2022 at 12:37:15AM -0500, Mario Limonciello wrote:
On 9/2/22 00:29, Greg KH wrote:
On Fri, Sep 02, 2022 at 03:00:26AM +0000, Limonciello, Mario wrote:
[Public]
Hi,
A sysfs file /sys/bus/thunderbolt/devices/domainX/iommu_dma_protection is exported from the kernel and used by userspace to make judgments on whether to automatically authorize PCIe tunnels for USB4 devices. Before kernel 5.19 this file was only populated on Intel USB4 and TBT3 controllers, but starting with 5.19 it also populates for non-Intel as well.
So that's a new kernel feature?
The sysfs file was there all along, but it always showed "0" for anything but Intel systems. This makes it work properly on everyone else.
This is accomplished by an assertion from the IOMMU subsystem that it's safe to do so by a combination of firmware and hardware.
Here is the patch series on top of 5.15.64:
3f6634d997dba8140b3a7cba01776b9638d70dff ed36d04e8f8d7b00db451b0fa56a54e8e02ec43e d0be55fbeb6ac694d15af5d1aad19cdec8cd64e5 f316ba0a8814f4c91e80a435da3421baf0ddd24c f1ca70717bcb4525e29da422f3d280acbddb36fe bfb3ba32061da1a9217ef6d02fbcffb528e4c8df 418e0a3551bbef5b221705b0e5b8412cdc0afd39 acdb89b6c87a2d7b5c48a82756e6f5c6f599f60a ea4692c75e1c63926e4fb0728f5775ef0d733888 86eaf4a5b4312bea8676fb79399d9e08b53d8e71
Can you please consider backporting them to 5.15.y+?
I don't understand why all of the string helpers are needed just for the last commit, are you sure this is all necessary?
The last commit (thunderbolt commit) uses one of them. That commit for the one of them doesn't come back cleanly, but catching all of them up does.
So I could potentially change the thunderbolt commit to not use the string helper, but figured this was cleaner.
And again, this feels like new features are being added that are much more than just a "new device id added". Why not just use 5.19 for this hardware?
Stuff like this is targeted towards businesses that would want to be using LTS kernels. In fact I heard "But on Intel we just plug in the dock and it just works" is what prompted the series in the first place.
It improves usability quite a bit because without it you need to know to manually change the sysfs file for your dock to work or you need to have GNOME installed and go and find the panel to change it.
With this sysfs file is showing the right value you get all that happening automatically.
I understand the wish to have hardware work on older kernel versions, but in looking over the full patch series here, it's not just a trivial addition. This is adding lots of things that were never in 5.15 to start with for AMD hardware (and touching other platform's code at the same time), which is fine for newer kernels, but not to backport to older ones.
Here's the overall diffstat of what you are asking for:
drivers/iommu/amd/amd_iommu_types.h | 4 ++++ drivers/iommu/amd/init.c | 3 +++ drivers/iommu/amd/iommu.c | 2 ++ drivers/iommu/dma-iommu.c | 5 +++++ drivers/iommu/intel/iommu.c | 2 ++ drivers/iommu/iommu.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++------------------------- drivers/thunderbolt/domain.c | 12 +++--------- drivers/thunderbolt/nhi.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ include/linux/iommu.h | 19 +++++++++++++++++++ include/linux/string_helpers.h | 25 +++++++++++++++++++++++++ include/linux/thunderbolt.h | 2 ++ lib/string_helpers.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 12 files changed, 221 insertions(+), 34 deletions(-)
The string helpers are trivial, but those iommu changes were not.
As proof of that, you missed some fixes in the kernel tree for the above requested commits that would have caused problems. Heck, even the string helpers needed a fix that you missed, so I was wrong in saying they were trivial!
So if I would have taken these commits as asked for, they might not have even worked properly and caused problems for people. So for that reason alone I would have had to reject this request.
Remember, stable kernels are not for "new hardware enablement", unlike how some distro kernels work. If you wanted this hardware to be supported for last year's stable kernel release, you all would have done the work back then to get it accepted as obviously you all had the hardware back then and knew it was going to be an issue.
Just point any user of this hardware to the latest kernel release, and all will be fine. And work on getting your new hardware supported upstream quicker please. That will prevent this issue from happening again in the future.
thanks,
greg k-h