On Mon, Jul 1, 2019 at 11:17 PM Pankaj Suryawanshi <pankajssuryawanshi@xxxxxxxxx> wrote: > > > > > On Mon, Jul 1, 2019 at 7:39 PM Robin Murphy <robin.murphy@xxxxxxx> wrote: >> >> On 28/06/2019 17:29, Pankaj Suryawanshi wrote: >> > On Wed, Jun 26, 2019 at 11:21 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: >> >> >> >> On Wed, Jun 26, 2019 at 10:12:45PM +0530, Pankaj Suryawanshi wrote: >> >>> [CC: linux kernel and Vlastimil Babka] >> >> >> >> The right list is the list for the DMA mapping subsystem, which is >> >> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx. I've also added that. >> >> >> >>>> I am writing driver in which I used DMA_ATTR_NO_KERNEL_MAPPING attribute >> >>>> for cma allocation using dma_alloc_attr(), as per kernel docs >> >>>> https://www.kernel.org/doc/Documentation/DMA-attributes.txt buffers >> >>>> allocated with this attribute can be only passed to user space by calling >> >>>> dma_mmap_attrs(). >> >>>> >> >>>> how can I mapped in kernel space (after dma_alloc_attr with >> >>>> DMA_ATTR_NO_KERNEL_MAPPING ) ? >> >> >> >> You can't. And that is the whole point of that API. >> > >> > 1. We can again mapped in kernel space using dma_remap() api , because >> > when we are using DMA_ATTR_NO_KERNEL_MAPPING for dma_alloc_attr it >> > returns the page as virtual address(in case of CMA) so we can mapped >> > it again using dma_remap(). >> >> No, you really can't. A caller of dma_alloc_attrs(..., >> DMA_ATTR_NO_KERNEL_MAPPING) cannot make any assumptions about the void* >> it returns, other than that it must be handed back to dma_free_attrs() >> later. The implementation is free to ignore the flag and give back a >> virtual mapping anyway. Any driver which depends on how one particular >> implementation on one particular platform happens to behave today is, >> essentially, wrong. > > > Here is the example that i have tried in my driver. > ///////////////code snippet///////////////////////////////////////////////////////////////////////// > > For CMA allocation using DMA API with DMA_ATTR_NO_KERNEL_MAPPING :- > > if(strcmp("video",info->name) == 0) > { > printk("Testing CMA Alloc %s\n", info->name); > info->dma_virt = dma_alloc_attrs(pmap_device, info->size, &phys, GFP_KERNEL, > DMA_ATTR_WRITE_COMBINE | DMA_ATTR_FORCE_CONTIGUOUS | DMA_ATTR_NO_KERNEL_MAPPING); > if (!info->dma_virt) { > pr_err("\x1b[31m" "pmap: cma: failed to alloc %s" "\x1b[0m\n", > info->name); > return 0; > } > __dma_remap(info->dma_virt, info->size, PAGE_KERNEL); // /*TO DO pgprot we will be taken from attr */ // we will use this only when virtual mapping is required. > virt = page_address(info->dma_virt); // will use this virtual when kernel mapping needed. > } > > For CMA free using DMA api with DMA_ATTR_NO_KERNEL_MAPPING:- > > if(strcmp("video",info->name) == 0) > { > printk("Testing CMA Release\n"); > __dma_remap(info->dma_virt, info->size, PAGE_KERNEL); > dma_free_attrs(pmap_device, info->size, info->dma_virt, phys, > DMA_ATTR_WRITE_COMBINE | DMA_ATTR_FORCE_CONTIGUOUS | DMA_ATTR_NO_KERNEL_MAPPING); > } > > Flow of Function calls :- > > 1. static void *__dma_alloc() // .want_vaddr = ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) == 0) > > 2.cma_allocator :- > i. static void *cma_allocator_alloc () > ii. static void *__alloc_from_contiguous() // file name :- ./arch/arm/mm/dma-mapping.c > if (!want_vaddr) > goto out; // condition true for DMA_ATTR_NO_KERNEL_MAPPING > > if (PageHighMem(page)) { > ptr = __dma_alloc_remap(page, size, GFP_KERNEL, prot, caller); > if (!ptr) { > dma_release_from_contiguous(dev, page, count); > return NULL; > } > } else { > __dma_remap(page, size, prot); > ptr = page_address(page); > } > > out: > *ret_page = page; // return page > return ptr; // nothing in ptr > } > iii. struct page *dma_alloc_from_contiguous() > iv. cma_alloc() > 3. dma_alloc () // returns > return args.want_vaddr ? addr : page; // returns page which is return by alloc_from_contiguous(). > > What wrong with this if we already know page is returning dma_alloc_attr(). > we can use dma_remap in our driver and free as freed in static void __free_from_contiguous (). > Please let me know if i missing anything. > >> > 2. We can mapped in kernel space using vmap() as used for ion-cma >> > https://github.com/torvalds/linux/tree/master/drivers/staging/android/ion >> > as used in function ion_heap_map_kernel(). >> > >> > Please let me know if i am missing anything. >> >> If you want a kernel mapping, *don't* explicitly request not to have a >> kernel mapping in the first place. It's that simple. > > > Do you mean do not use dma-api ? because if i used dma-api it will give you mapped virtual address. > or i have to use directly cma_alloc() in my driver. // if i used this approach i need to reserved more vmalloc area. > > Any help would be appreciated. >> >> >> Robin.
