Re: [PATCH] spi: Assign dummy scatterlist to unidirectional transfers

[Andy Shevchenko]

Wed, May 29, 2024 at 11:42:35AM -0400, Nícolas F. R. A. Prado kirjoitti:
> From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> 
> Commit 8cc3bad9d9d6 ("spi: Remove unneded check for orig_nents")
> introduced a regression: unmapped data could now be passed to the DMA
> APIs, resulting in null pointer dereferences. Commit 9f788ba457b4 ("spi:
> Don't mark message DMA mapped when no transfer in it is") and commit
> da560097c056 ("spi: Check if transfer is mapped before calling DMA sync
> APIs") addressed the problem, but only partially. Unidirectional
> transactions will still result in null pointer dereference. To prevent
> that from happening, assign a dummy scatterlist when no data is mapped,
> so that the DMA API can be called and not result in a null pointer
> dereference.

I feel that with this the da560097c056 ("spi: Check if transfer is mapped
before calling DMA sync APIs") can be reverted as unneeded. Nícolas, can
you check that? If it works, we better revert the unneeded checks.

-- 
With Best Regards,
Andy Shevchenko