Re: [PATCH v2 3/3] doc: Add ABI documentation for uio_pci_sva driver sysfs attributes

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Sep 26, 2025 at 01:57:58PM +0800, yaxing guo wrote:
> Hi, Greg,
> 
> Thank you for your feedback.
> 
> On 9/25/2025 8:32 PM, Greg KH wrote:
> > On Thu, Sep 25, 2025 at 06:40:18PM +0800, Yaxing Guo wrote:
> > > Add ABI documentation for the sysfs interface provided by the
> > > uio_pci_sva driver, specifically the 'pasid' attribute.
> > > 
> > > The 'pasid' attribute exposes the Process Address Space ID (PASID)
> > > assigned by the IOMMU to the device for use with Shared Virtual
> > > Addressing (SVA). User-space UIO applications read this attribute
> > > to obtain the PASID and program it into the device's configuration
> > > registers, enabling the device to perform DMA using user-space
> > > virtual addresses.
> > > 
> > > This attribute appears under:
> > > /sys/bus/pci/drivers/uio_pci_sva/<pci_dev>/pasid
> > > 
> > > Signed-off-by: Yaxing Guo <guoyaxing@bosc.ac.cn>
> > > ---
> > >   .../ABI/testing/sysfs-driver-uio_pci_sva-pasid    | 15 +++++++++++++++
> > >   1 file changed, 15 insertions(+)
> > >   create mode 100644 Documentation/ABI/testing/sysfs-driver-uio_pci_sva-pasid
> > > 
> > > diff --git a/Documentation/ABI/testing/sysfs-driver-uio_pci_sva-pasid b/Documentation/ABI/testing/sysfs-driver-uio_pci_sva-pasid
> > > new file mode 100644
> > > index 000000000000..a6afa8c2775c
> > > --- /dev/null
> > > +++ b/Documentation/ABI/testing/sysfs-driver-uio_pci_sva-pasid
> > > @@ -0,0 +1,15 @@
> > > +What:		/sys/bus/pci/drivers/uio_pci_sva/<pci_dev>/pasid
> > > +Date:		September 2025
> > > +Contact:	Yaxing Guo <guoyaxing@bosc.ac.cn>
> > > +Description:
> > > +		Process Address Space ID (PASID) assigned by IOMMU driver to
> > > +		the device for use witch Shared Virtual Addressing (SVA).
> > 
> > "with", not "witch", right?
> > 
> > > +
> > > +		This read-only attribute exposes the PASID allocated by the
> > > +		IOMMU driver during sva device binding.
> > > +
> > > +		User-space UIO applications must read this attribute to
> > > +		obtain the PASID and program it into the device's configuration
> > > +		registers. This enables the device to perform DMA using
> > > +		user-space virtual address, with address translation handled
> > > +		by IOMMU.
> > 
> > What is a PASID?  What format is it in?
> > 
> > How can it then be used in userspace?  What is a "device configuration
> > register" and what api uses it?
> > 
> > And where is the userspace code that interacts with all of this?
> > 
> 
> The UIO userspace code is inherently tied to the hardware and its
> register layout. Therefore, there isn't a single open-source userspace
> implementation(In my job, this is for a simple FPAG-based test device used
> for iommu-sva functionality validation).

That's ok to publish it, userspace UIO drivers need to also be released
under an open license as they are explicitly tied to the kernel
interface.  Without that, it's hard to judge if the api is correct or
not.

thanks,

greg k-h