using ioremap() memory in dma_map_sg()

using ioremap() memory in dma_map_sg()

[Olga Kitaina]

Hi.
As part of our driver, we want to have some device memory to be 
available to other devices via the DMA-BUF subsystem. The device memory 
is managed by genpool, and mapped from the sram driver via ioremap_wc(). 
We initially used sg_set_buf() with the virtual address returned from 
gen_pool_dma_alloc(), but it seems like the wrong thing to do, since the 
virt_addr_valid() check fails. Attempting to use vmalloc_to_page() 
results in a failure down the line, such as:

Unable to handle kernel paging request at virtual address ba405000
Backtrace:
(dma_cache_maint_page) from (__dma_page_dev_to_cpu+0x88/0x108)
(__dma_page_dev_to_cpu) from (arm_dma_map_page+0x5c/0x60)
(arm_dma_unmap_page) from (arm_dma_map_sg+0x64/0x8c)
(arm_dma_unmap_sg) from(foo_dmabuf_map+0x60/0x8c [foo])

Is there an appropriate way to put an ioremapped buffer into an SG table?

Thanks,
Olga.

Re: using ioremap() memory in dma_map_sg()

[Andy Shevchenko]

On Mon, Nov 19, 2018 at 6:31 PM Olga Kitaina <okitain@elvees.com> wrote:
>
> Hi.
> As part of our driver, we want to have some device memory to be
> available to other devices via the DMA-BUF subsystem. The device memory
> is managed by genpool, and mapped from the sram driver via ioremap_wc().
> We initially used sg_set_buf() with the virtual address returned from
> gen_pool_dma_alloc(), but it seems like the wrong thing to do, since the
> virt_addr_valid() check fails. Attempting to use vmalloc_to_page()
> results in a failure down the line, such as:
>
> Unable to handle kernel paging request at virtual address ba405000
> Backtrace:
> (dma_cache_maint_page) from (__dma_page_dev_to_cpu+0x88/0x108)
> (__dma_page_dev_to_cpu) from (arm_dma_map_page+0x5c/0x60)
> (arm_dma_unmap_page) from (arm_dma_map_sg+0x64/0x8c)
> (arm_dma_unmap_sg) from(foo_dmabuf_map+0x60/0x8c [foo])
>
> Is there an appropriate way to put an ioremapped buffer into an SG table?

Olga, I'm not sure you really want DMA-BUF subsystem for your task.
Anyway, I Cc'ed to couple of maintainers, hope they can help you.

-- 
With Best Regards,
Andy Shevchenko