[PATCH i-g-t v2 2/4] lib/intel_vram: Add library for VRAM accesses

[Bernatowicz, Marcin]

On 8/27/2025 4:49 PM, Lukasz Laguna wrote:
> Prepare a library with helpers to map and unmap VRAM BAR region and
> perform read/write operations.
> 
> Signed-off-by: Lukasz Laguna <lukasz.laguna at intel.com>
> ---
> v2:
> - drop O_SYNC flag (Marcin)
> - use uint64_t for BAR size and offsets (Marcin)
> - refactor functions - return int and fill the pointers (Marcin)
> - check the provided offset and length in intel_vram_mmap (Marcin)
> ---
>   lib/intel_vram.c | 189 +++++++++++++++++++++++++++++++++++++++++++++++
>   lib/intel_vram.h |  22 ++++++
>   lib/meson.build  |   1 +
>   3 files changed, 212 insertions(+)
>   create mode 100644 lib/intel_vram.c
>   create mode 100644 lib/intel_vram.h
> 
> diff --git a/lib/intel_vram.c b/lib/intel_vram.c
> new file mode 100644
> index 000000000..9be2ba3ac
> --- /dev/null
> +++ b/lib/intel_vram.c
> @@ -0,0 +1,189 @@
> +// SPDX-License-Identifier: MIT
> +/*
> + * Copyright © 2025 Intel Corporation
> + */
> +
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <inttypes.h>
> +#include <sys/mman.h>
> +#include <sys/stat.h>
> +
> +#include "igt_core.h"
> +#include "igt_sriov_device.h"
> +#include "intel_vram.h"
> +
> +static int intel_vram_open_bar(int pf_fd, unsigned int vf_num, int mode)
> +{
> +	int sysfs, fd;
> +
> +	sysfs = igt_sriov_device_sysfs_open(pf_fd, vf_num);
> +	if (sysfs < 0) {
> +		igt_debug("Failed to open sysfs for VF%d: %s\n", vf_num, strerror(errno));
> +		return -1;
> +	}
> +
> +	fd = openat(sysfs, "resource2", mode);
> +	if (fd < 0)
> +		igt_debug("Failed to open resource2 for VF%d: %s\n", vf_num, strerror(errno));
> +
> +	close(sysfs);
> +
> +	return fd;
> +}
> +
> +/**
> + * intel_vram_bar_size - Get the size of the VRAM BAR
> + * @pf_fd: PF device file descriptor
> + * @vf_num: VF number (1-based), or 0 for the PF
> + * @size: pointer to store VRAM BAR size
> + *
> + * Opens the VRAM BAR file descriptor for the specified device and retrieves
> + * its size by using fstat().
> + *
> + * Return: 0 on success, or negative value on failure.
> + */
> +int intel_vram_bar_size(int pf_fd, unsigned int vf_num, uint64_t *size)
> +{
> +	int fd, ret = 0;
> +	struct stat st;
> +
> +	if (!size)
> +		return -EINVAL;
> +
> +	fd = intel_vram_open_bar(pf_fd, vf_num, O_RDONLY);
> +	if (fd < 0)
> +		return fd;
> +
> +	if (fstat(fd, &st))
> +		ret = -errno;
> +	else
> +		*size = (uint64_t)st.st_size;
> +
> +	close(fd);
> +
> +	return ret;
> +}
> +
> +/**
> + * intel_vram_mmap - Map VRAM BAR region
> + * @pf_fd: PF device file descriptor
> + * @vf_num: VF number (1-based), or 0 for the PF
> + * @offset: Offset (in bytes) within the BAR to begin the mapping
> + * @length: Number of bytes to map
> + * @prot: Memory protection flags
> + * @map: pointer to vram_mapping struct to store address and size of the mapping
> + *
> + * Maps a PF or VF VRAM BAR into user space using mmap(). On error, it sets the
> + * mapping address to NULL and the mapping size to 0.
> + *
> + * Return: 0 on success, or negative value on failure.
> + */
> +int intel_vram_mmap(int pf_fd, unsigned int vf_num, uint64_t offset, size_t length,
> +		    int prot, struct vram_mapping *map)
> +{
> +	uint64_t bar_size, end;
> +	int fd, ret = 0;
> +	void *addr;
> +
> +	if (!map)
> +		return -EINVAL;
> +
> +	map->addr = NULL;
> +	map->size = 0;
> +
> +	if (!length)
> +		return 0;
> +
> +	ret = intel_vram_bar_size(pf_fd, vf_num, &bar_size);
> +	if (ret)
> +		return ret;
> +
> +	end = offset + length;
> +	if (end < offset || end > bar_size)
> +		return -EINVAL;
> +
> +	fd = intel_vram_open_bar(pf_fd, vf_num, (prot & PROT_WRITE) ? O_RDWR : O_RDONLY);
> +	if (fd < 0)
> +		return fd;
> +
> +	addr = mmap(NULL, length, prot, MAP_SHARED, fd, (off_t)offset);
> +	if (addr == MAP_FAILED) {
> +		ret = -errno;
> +		goto end;
> +	}
> +
> +	map->addr = addr;
> +	map->size = length;
> +end:
> +	close(fd);
> +
> +	return ret;
> +}
> +
> +/**
> + * intel_vram_munmap - Unmap previously mapped VRAM region
> + * @m: Pointer to a vram_mapping struct representing the mapped region
> + *
> + * Unmaps the user-space memory region previously mapped by intel_vram_mmap().
> + *
> + * Return: 0 on success, or negative value on failure.
> + */
> +int intel_vram_munmap(struct vram_mapping *m)
> +{
> +	int ret;
> +
> +	ret = munmap(m->addr, m->size);
> +	if (ret < 0)
> +		igt_debug("Failed munmap %p: %s\n", m->addr, strerror(errno));
> +
> +	return ret;
> +}
> +
> +/**
> + * intel_vram_read8 - Read 8-bit value from a mapped VRAM region
> + * @m: Pointer to a vram_mapping struct representing the mapped region
> + * @offset: Offset (in bytes) to read from
> + *
> + * Reads a single 8-bit value from the specified offset in the mapped VRAM.
> + *
> + * Return: The 8-bit value read from the given offset.
> + */
> +uint8_t intel_vram_read8(struct vram_mapping *m, size_t offset)

NIT: can be const struct vram_mapping *m (and in all helpers below)

> +{
> +	igt_assert(offset < m->size);
> +
> +	return READ_ONCE(*((uint8_t *)m->addr + offset));
> +}
> +
> +/**
> + * intel_vram_write8 - Write 8-bit value to a mapped VRAM region
> + * @m: Pointer to a vram_mapping struct representing the mapped region
> + * @offset: Offset (in bytes) to write to
> + * @value: The 8-bit value to write
> + *
> + * Writes a single 8-bit value to the specified offset in the mapped VRAM.
> + */
> +void intel_vram_write8(struct vram_mapping *m, size_t offset, uint8_t value)
> +{
> +	igt_assert(offset < m->size);
> +
> +	WRITE_ONCE(*((uint8_t *)m->addr + offset), value);
> +}
> +
> +/**
> + * intel_vram_write_readback8 - Write and then read back an 8-bit value
> + * @m: Pointer to a vram_mapping struct representing the mapped region
> + * @offset: Offset (in bytes) to write to and read from
> + * @value: The 8-bit value to write
> + *
> + * Writes an 8-bit value to the specified offset in the mapped VRAM and
> + * reads it back to verify if the write was successful.
> + *
> + * Return: The 8-bit value read back from the given offset.
> + */
> +uint8_t intel_vram_write_readback8(struct vram_mapping *m, size_t offset, uint8_t value)
> +{
> +	intel_vram_write8(m, offset, value);
> +	return intel_vram_read8(m, offset);
> +}
> diff --git a/lib/intel_vram.h b/lib/intel_vram.h
> new file mode 100644
> index 000000000..47ed2f2ca
> --- /dev/null
> +++ b/lib/intel_vram.h
> @@ -0,0 +1,22 @@
> +/* SPDX-License-Identifier: MIT */
> +/*
> + * Copyright © 2025 Intel Corporation
> + */
> +
> +#ifndef __INTEL_VRAM_H__
> +#define __INTEL_VRAM_H__
> +
> +struct vram_mapping {
> +	void *addr; /* Pointer to the mapped VRAM */
> +	size_t size; /* Size of the mapped VRAM region */
> +};
> +
> +int intel_vram_bar_size(int pf_fd, unsigned int vf_num, uint64_t *size);
> +int intel_vram_mmap(int pf_fd, unsigned int vf_num, uint64_t offset, size_t length,
> +		    int prot, struct vram_mapping *map);
> +int intel_vram_munmap(struct vram_mapping *m);
> +uint8_t intel_vram_read8(struct vram_mapping *m, size_t offset);
> +void intel_vram_write8(struct vram_mapping *m, size_t offset, uint8_t value);
> +uint8_t intel_vram_write_readback8(struct vram_mapping *m, size_t offset, uint8_t value);
> +
> +#endif	/* __INTEL_VRAM_H__ */
> diff --git a/lib/meson.build b/lib/meson.build
> index f078dad4e..fcdfca42a 100644
> --- a/lib/meson.build
> +++ b/lib/meson.build
> @@ -70,6 +70,7 @@ lib_sources = [
>   	'intel_mocs.c',
>   	'igt_multigpu.c',
>   	'intel_pat.c',
> +	'intel_vram.c',
>   	'ioctl_wrappers.c',
>   	'media_spin.c',
>   	'media_fill.c',

LGTM,
Reviewed-by: Marcin Bernatowicz <marcin.bernatowicz at linux.intel.com>