Arch=x86_64
I am working through a DMA solution following the process outlined in this question, Direct Memory Access in Linux
My call to ioremap successfully returns with an address, pt.
In my call to remap_pfn_range I use, virt_to_phys(pt) >> PAGE_SHIFT, to specify the pfn of the area generated by the ioremap call.
When the userspace application using mmap executes and the call to remap_pfn_range is made, the machine crashes. I assume the mapping is off and I am forcing the system to use memory that is already allocated (screen glitches before exit), however I'm not clear on where the mismatch is occurring. The system has 4 Gigs of Ram and I reserved 2Gigs by using the kernel boot option mem=2048M.
I use BUFFER_SIZE=1024u*1024u*1024u and BUFFER_OFFSET=2u*1024u*1024u*1024u.
putting these into pt=ioremap(BUFFER_SIZE,BUFFER_OFFSET) I believe pt should equal a virtual address to the physical memory located at the 2GB boundary up to the 3GB boundary. Is this assumption accurate?
When I execute my kernel module, but I change my remap_pfn_range to use vma->vm_pgoff>>PAGE_SHIFT as the target pfn the code executes with no error and I can read and write to the memory. However this is not using the reserved physical memory that I intended.
Since everything works when using vma->vm_pgoff>>PAGE_SHIFT I believe my culprit is between my ioremap and the remap_pfn_range
Thanks for any suggestions!
The motivation behind the use of this kernel module is the need for large contiguous buffers for DMA from a PCI device. In this application, recompiling the kernel isn't an option so I'm trying to accomplish it with a module + hardware.
