[SOLVED] Access GPU as PCI device

Issue

I am new to the GPU OS kernelspace world. I would like to access GPU memory as a PCI device through its memory exposed on the BAR using for exmaple dev_alloc () which is allocating memory and returns an address to this address.

void *addr;
addr = dev_alloc ()
//check that the allocated address is in the device bar range 
if(In_bar_range(virt_to_phy(addr))) {
WRITE_ONCE(addr[0], 0);
READ_ONCE(addr[0]);
}

I also tried mapping using pci_iomap as follows

  void* __iomap map;
  u32 val;
  map=pci_iomap(pci_dev,0,8);
  iowrite8(0, map);
  val=ioread8(map);
  dev_info(&dev " value = %ud ", val);

Trying to read from the values fails. It does not return 0. It returns a garbage value. I do not know whether there is a problem in addressing translation (IO_MMU) or if I am missing some kind of synchronization between the CPU and the GPU or if it is another problem?

Solution

Not exactly sure what you already have to work with, and it might vary based on the kernel version, but I'm assuming you already have a pointer to the device.

If you don't already have one, you will first need to obtain an iomem mapping through pci_iomap() (asm/pci_iomap.h) passing a pointer to the device (struct pci_dev) and the PCI BAR number. Then, as explained in DMA-API-HOWTO you should be able to read/write through this mapping using one of the io{read,write}*() functions defined in asm/iomap.h.

Answered By - Marco Bonelli

Answer Checked By - Marie Seifert (WPSolving Admin)