linux-kernel - [PATCH 0/3] uio/dma-buf: Give UIO users access to DMA addresses.

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Message-Id: <20250410-uio-dma-v1-0-6468ace2c786@bootlin.com>
Date: Thu, 10 Apr 2025 16:53:17 +0200
From: Bastien Curutchet <bastien.curutchet@...tlin.com>
To: Sumit Semwal <sumit.semwal@...aro.org>, 
 Christian König <christian.koenig@....com>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
 linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org, 
 Bastien Curutchet <bastien.curutchet@...tlin.com>
Subject: [PATCH 0/3] uio/dma-buf: Give UIO users access to DMA addresses.

Hi all,

Many UIO users performing DMA from their UIO device need to access the
DMA addresses of the allocated buffers. There are out-of-tree drivers
that allow to do it but nothing in the mainline.

I know DMA shouldn't be handled by userspace but, IMHO, since UIO
drivers exist, it would be better if they offered a way of doing this.

This patch series use the dma-heap framework which already allows
userspace to allocate DMA buffers. I tried to avoid 'polluting' the
existing heaps to prevent inappropriate uses of this new feature by
introducing a new UIO heap, which is the only one implementing this
behavior.

PATCH 1 allows the creation of heaps that don't implement map/unmap_buf
operations as UIO heap doesn't use them.
PATCH 2 adds the DMA_BUF_IOCTL_GET_DMA_ADDR which transmits the DMA
addresses to userspace.
PATCH 3 implements the UIO heap.

It has been tested with the uio_pci_generic driver on a PowerPC.

Signed-off-by: Bastien Curutchet <bastien.curutchet@...tlin.com>
---
Bastien Curutchet (3):
      dma-buf: Allow heap that doesn't provide map_buf/unmap_buf
      dma-buf: Add DMA_BUF_IOCTL_GET_DMA_ADDR
      uio: Add UIO_DMABUF_HEAP

 drivers/dma-buf/dma-buf.c    |  29 +++++++++--
 drivers/uio/Kconfig          |   9 ++++
 drivers/uio/Makefile         |   1 +
 drivers/uio/uio.c            |   4 ++
 drivers/uio/uio_heap.c       | 120 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/dma-buf.h      |   1 +
 include/linux/uio_driver.h   |   2 +
 include/uapi/linux/dma-buf.h |   1 +
 8 files changed, 164 insertions(+), 3 deletions(-)
---
base-commit: 5f13fa25acaa4f586aaed12efcf7436e004eeaf2
change-id: 20250408-uio-dma-9b011e9e7f0b

Best regards,
-- 
Bastien Curutchet <bastien.curutchet@...tlin.com>