On 12/07/2019 19:30, Pankaj Suryawanshi wrote:
Hello,
When we allocate cma memory using dma_alloc_attr using
DMA_ATTR_NO_KERNEL_MAPPING attribute. It will return physical address
without virtual mapping and thats the use case of this attribute. but lets
say some vpu/gpu drivers required virtual mapping of some part of the
allocation. then we dont have anything to remap that allocated memory to
virtual memory. and in 32-bit system it difficult for devices like android
to work all the time with virtual mapping, it degrade the performance.
For Example :
Lets say 4k video allocation required 300MB cma memory but not required
virtual mapping for all the 300MB, its require only 20MB virtually mapped
at some specific use case/point of video, and unmap virtual mapping after
uses, at that time this functions will be useful, it works like ioremap()
for cma_alloc() using dma apis.
Hmm, is there any significant reason that this case couldn't be handled
with just get_vm_area() plus dma_mmap_attrs(). I know it's only
*intended* for userspace mappings, but since the basic machinery is there...
Robin.
/*
* function call(s) to create virtual map of given physical memory
* range [base, base+size) of CMA memory.
*/
void *cma_remap(__u32 base, __u32 size)
{
struct page *page = phys_to_page(base);
void *virt;
pr_debug("cma: request to map 0x%08x for size 0x%08x\n",
base, size);
size = PAGE_ALIGN(size);
pgprot_t prot = get_dma_pgprot(DMA_ATTR, PAGE_KERNEL);
if (PageHighMem(page)){
virt = dma_alloc_remap(page, size, GFP_KERNEL, prot,
__builtin_return_address(0));
}
else
{
dma_remap(page, size, prot);
virt = page_address(page);
}
if (!virt)
pr_err("\x1b[31m" " cma: failed to map 0x%08x" "\x1b[0m\n",
base);
else
pr_debug("cma: 0x%08x is virtually mapped to 0x%08x\n",
base, (__u32) virt);
return virt;
}
/*
* function call(s) to remove virtual map of given virtual memory
* range [virt, virt+size) of CMA memory.
*/
void cma_unmap(void *virt, __u32 size)
{
size = PAGE_ALIGN(size);
unsigned long pfn = virt_to_pfn(virt);
struct page *page = pfn_to_page(pfn);
if (PageHighMem(page))
dma_free_remap(virt, size);
else
dma_remap(page, size, PAGE_KERNEL);
pr_debug(" cma: virtual address 0x%08x is unmapped\n",
(__u32) virt);
}
This functions should be added in arch/arm/mm/dma-mapping.c file.
Please let me know if i am missing anything.
Regards,
Pankaj
