linux-kernel - Re: [PCI Driver Help] Locking Pages of a running process

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Message-ID: <19966.65175.273917.314279@pilspetsen.it.uu.se>
Date:	Mon, 20 Jun 2011 10:02:31 +0200
From:	Mikael Pettersson <mikpe@...uu.se>
To:	newton mailinglist <newtonmailinglist@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PCI Driver Help] Locking Pages of a running process

newton mailinglist writes:
 > Hi,
 > 
 > I have written a PCI driver for my device. The device is an FPGA which
 > is configured with a design that allows it to have direct access to
 > memory of a host computer to which the fpga board is connected. My
 > device driver is responsible for translating virtual addresses to
 > physical addresses and sending these to the FPGA so the DMA unit in
 > the FPGA can directly access pages in memory.
 > 
 > I have a C program which uses the driver to open this PCI device and
 > then sends a command to the device, so it can begin accessing
 > memory(for some calculations done in the fpga). This is done via
 > IOCTL. The FPGA sends an interrupt when its done. However my program
 > does not wait for the FPGA but instead resumes execution immmediately
 > after the IOCTL call returns. If the FPGA has a virtual address which
 > it needs to translate, it interrupts my PCI driver and I want to
 > translate this address in the interrupt handler and write back the
 > translated address to the device using memory mapped I/O.
 > 
 > The issue is that when my driver gets the virtual address, it attempts
 > to lock the user space pages first(those of the running C program) in
 > memory using get_user_pages() and then translates the address using
 > pci_map_page(). Pinning the pages in memory is needed as the fpga will
 > access them later using DMA. Here is the code I use   :

Instead of sending user-space pages from an application to the driver,
expecting the driver to do address space translations and locking,
your driver should implement mmap() and user-space should get its I/O
buffers by mmap()ing the device.
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