On 9/25/26 07:28, Jason Gunthorpe wrote:
On Fri, Sep 25, 2026 at 09:20:02AM +0200, Joerg Roedel wrote:
On Thu, Sep 24, 2026 at 07:50:18PM -0300, Jason Gunthorpe wrote:
Why does the GPU driver have to request this? Why can't the iommu
driver know that this is a special device that can use this magic fast
path and then auto set it when identity is asked for?
This is a layering violation either way. Either the IOMMU driver needs to poke
into device details and their relations or the device driver needs to poke into
IOMMU details.
There are no device details, this is just a module option in the gpu
driver.
Well the GPU driver has knowledge whether it's a GPU inside of an APU to
decide if it's valid. That information is part of the discovery table
setup.
This is not perfect but to some degree unavoidable with these highly integrated
SOCs.
This is exactly the sort of hacky thing ACPI should describe so the
drivers can just turn things on automatically.
Who is ever going to track down and figure out it is OK to set these
kinds of module options in the first place? There is general negative
sentiment in the kernel to doing things like this with modue options.
How does Windows do it? There certainly isn't a "module option" there?
Jason
This specific one I don't know; but these kinds of things usually end up
in knobs in a UI that plumb some IPC deep into the driver stack.
