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 with Shared Virtual Addressing (SVA).

		This read-only attribute exposes the PASID (A 20-bit identifier
		used in PCIe Address Translation Services and iommu table walks)
		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.

		UIO User-space applications must:
		- Opening device and Mapping the device's register space via /dev/uioX
		(This triggers the IOMMU driver to allocate the PASID)
		- Reading the PASID from sysfs
		- Writing the PASID to a device-specific register (with example offset)
		The code may be like:

		map = mmap(..., "/dev/uio0", ...);

		f = fopen("/sys/.../pasid", "r");
		fscanf(f, "%d", &pasid);

		map[REG_PASID_OFFSET] = pasid;
