Is it possible to MMAP a PCI BAR memory? - driver

Question

I want to user access memory from a PCIe board which provides a 1GB memory with BAR0.
Currently I use only read and write functionality of my character device driver, which is VERY slow (1MB/s read and 16MB/s write) on a 8x PCIe Gen3.
static ssize_t
MPD_read(
struct file *filp,
char *buffer,
size_t bufferSize,
loff_t *offset )
{
unsigned long unusedBytes = copy_to_user(
( void * ) buffer,
MPD_AdapterBoard.bars[ 0 ].barHWAddress,
bufferSize );
return 0;
}
static ssize_t
MPD_write(
struct file *filp,
const char *buffer,
size_t bufferSize,
loff_t *offset )
{
unsigned long unusedBytes = copy_from_user(
MPD_AdapterBoard.bars[ 0 ].barHWAddress,
( void * ) buffer,
bufferSize );
return 0;
}
Is it possible to use the MMAP (with the .mmap file operation) to get more speed ?
Or is DMA the only option ?
Thanks in advance!
/Jesko

Answer 1

I found out how it's working:
static int
MPD_mmap(
struct file *filp,
struct vm_area_struct *vma )
{
unsigned long offset;
offset = vma->vm_pgoff << PAGE_SHIFT;
if (( offset + ( vma->vm_end - vma->vm_start )) > MPD_AdapterBoard.bars[ 0 ].barSizeInBytes )
{
return -EINVAL;
}
offset += ( unsigned long ) MPD_AdapterBoard.bars[ 0 ].mmioStart;
vma->vm_page_prot = pgprot_noncached( vma->vm_page_prot );
if ( io_remap_pfn_range(vma, vma->vm_start, offset >> PAGE_SHIFT, vma->vm_end - vma->vm_start, vma->vm_page_prot ))
{
return -EAGAIN;
}
return 0;
}
Attention: This is work in progress, so error checking is fairly limited.
In the hope to help someone here, the complete code can be downloaded including a test program from here: https://github.com/jesko42/minipci