[SOLVED] Get DPRAM mapped location in Linux

Get DPRAM mapped location in Linux

I have an old PCI device that uses DPRAM. I think Linux is supposed to automatically map the DPRAM to a location in memory - but I'm not sure of this. I found /proc/iomem that may contain the mapping. But I don't know how to identify my PCI device based on what's in /proc/iomem.

I have two questions. First, is /proc/iomem the right place to be looking? Second, how do I interpret what's in /proc/iomem to know what the right address is?

I called sudo cat /proc/iomem. The output looked like:

fc800000-fe7fffff : PCI Bus 0000:00
  fd000000-fd69ffff : pnp 00:0d
  fd6a0000-fd6affff : INT3450:00
    fd6a0000-fd6affff : INT3450:00 INT3450:00
  fd6b0000-fd6bffff : INT3450:00

But I don't know how to interpret everything after the : on each line.

Solution

You are correct that /proc/iomem shows the mapping of PCI(e) memory (and different things) into linearly addressable memory.

The format of iomem is (among other things):

<addr1>-<addr2> : <component>

Here, <component> can be

a PCI address (e.g. 0000:00:08:0)
plug & play memory region (pnp) that can be dynamically allocated
ACPI tables, kernel memory, USBC memory, system rom, ...

For your purpose you can use the lspci command to identify your PCI device address to find the memory ranges it is mapped to.

For example, on my system I can run lspci and see

$ lspci
[...]
01:00.1 Audio device: NVIDIA Corporation Device 10fa (rev a1)
[...]

Now I know that my NVIDIA audio device has PCI address 01:00.1 which I can use to find the memory region in /proc/iomem:

$ sudo cat /proc/iomem  | grep '01:00.1'
    ae000000-ae003fff : 0000:01:00.1