Leon Romanovsky <[email protected]> writes:
> On Tue, Jul 21, 2026 at 07:50:10PM +0530, Aneesh Kumar K.V wrote:
>> Leon Romanovsky <[email protected]> writes:
>>
>> > On Fri, Jul 17, 2026 at 11:34:19PM +0530, Aneesh Kumar K.V (Arm) wrote:
....
>> >> static void *dma_direct_alloc_no_mapping(struct device *dev, size_t size,
>> >> @@ -247,8 +246,11 @@ void *dma_direct_alloc(struct device *dev, size_t
>> >> size,
>> >> * the atomic pools instead if we aren't allowed block.
>> >> */
>> >> if ((remap || force_dma_unencrypted(dev)) &&
>> >> - dma_direct_use_pool(dev, gfp))
>> >> - return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
>> >> + dma_direct_use_pool(dev, gfp)) {
>> >> + page = dma_direct_alloc_from_pool(dev, size, dma_handle,
>> >> + &ret, gfp);
>> >> + return page ? ret : NULL;
>> >
>> > Sorry for joining the discussion late, but the line above caught my
>> > attention.
>> >
>> > Why do we need both ret and page? We can derive cpu_addr from page and
>> > vice versa. Do we really need the &ret parameter? Or, more generally, do
>> > we really need "struct page *"?
>> >
>> > static struct page *__dma_alloc_from_pool(struct device *dev, size_t size,
>> > struct gen_pool *pool, void **cpu_addr,
>> > bool (*phys_addr_ok)(struct device *, phys_addr_t, size_t))
>> > {
>> > ...
>> > *cpu_addr = (void *)addr;
>> > memset(*cpu_addr, 0, size);
>> > return pfn_to_page(__phys_to_pfn(phys));
>> > }
>> >
>> > Why
>> >
>>
>> With CONFIG_DMA_DIRECT_REMAP the cpu_addr can be different from
>> page_address.
>
> Can you please point to the code there it can happen?
> __dma_alloc_from_pool() has direct connection between physical address
> and struct page.
>
dma_direct_alloc -> remap = IS_ENABLED(CONFIG_DMA_DIRECT_REMAP);
if ((remap && dma_direct_use_pool(dev, gfp)) {
page = dma_direct_alloc_from_pool(dev, size,
..
__dma_alloc_from_pool ->
addr = gen_pool_alloc(pool, size);
if (!addr)
We expand the pool as below..
atomic_pool_expand ->
#ifdef CONFIG_DMA_DIRECT_REMAP
addr = dma_common_contiguous_remap(page, pool_size,
pgprot_decrypted(pgprot_dmacoherent(PAGE_KERNEL)),
__builtin_return_address(0));
if (!addr)
goto free_page;
#else
addr = page_to_virt(page);
#endif
-aneesh
