# \[PATCH v2 0/7\] Stop losing firmware-set DMA masks

- From: Robin Murphy \<robin.murphy@arm.com\>
- Date: 2018-07-27 10:55:35 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2018/07/8771684
- Thread: https://ratatoskr.run/linux-arm-kernel/2018/07/8771456/t.md

```text
Hi Grygorii,

Thanks for the report.

On 27/07/18 00:45, Grygorii Strashko wrote:
[...]
> With this series applied I can't boot TI ARM32 am574x-idk any more.
> 
> And log output is full of "DMA mask not set" -

That's somewhat expected - as the relevant commit message mentions, 
there will be bugs flushed out by this change, but the point is to fix 
them :)

> nobody sets dma_mask for platform bus in case of OF boot :(

Right, after a brief investigation, that one turns out to be nice and 
straightforward to explain and fix; I'll write up the patch shortly.

[...]
> [    3.793493] ti-qspi 4b300000.qspi: dma_alloc_coherent failed, using PIO mode
> [    3.801088] Unable to handle kernel NULL pointer dereference at virtual address 00000080
[...]
> [    4.602777] [<c04d87a4>] (omap_dma_write) from [<c04d8dc0>] (omap_dma_start_desc+0x78/0x150)
> [    4.611258] [<c04d8d48>] (omap_dma_start_desc) from [<c04d9028>] (omap_dma_issue_pending+0x90/0x98)
> [    4.620347]  r9:ed002780 r8:00000000 r7:00000010 r6:ee2bdd00 r5:ee2bdd4c r4:ee2bdd00
> [    4.628130] [<c04d8f98>] (omap_dma_issue_pending) from [<c0608d1c>] (ti_qspi_dma_xfer+0x8c/0x13c)
> [    4.637039]  r5:00000000 r4:ee7e1b28
> [    4.640636] [<c0608c90>] (ti_qspi_dma_xfer) from [<c06090b0>] (ti_qspi_exec_mem_op+0x2e4/0x32c)

Hooray, a real bug! Since dma_alloc_coherent() could have failed due to 
lack of memory or any other reason, that's not even directly related to 
this change, we've simply helped uncover it. I guess that PIO fallback 
path hasn't been tested recently, because it clearly doesn't work. It 
would be good if someone who knows the ti-qspi driver and has the means 
to test it could figure that one out before also adding the missing 
dma_set_coherent_mask() call.

Robin.
```