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SubjectRe: [PATCH] spi: a3700: fix hang caused by a3700_spi_transfer_one_fifo()
2020年6月30日(火) 20:11 Mark Brown <broonie@kernel.org>:
>
> On Tue, Jun 30, 2020 at 02:44:21AM +0900, Daisuke Yamane wrote:
> > transfer_one() must call spi_finalize_current_transfer() before
> > returning to inform current transfer has finished. Otherwise spi driver
> > doesn't issue next transfer, and hang.
>
> To be clear it can also return a positive value and then finalize later,
> there's no need to finalize before returning (otherwise finalizing would
> be a bit redundant) and if the driver doesn't return a positive value
> there should be no need to finalize at all.
>
> > However a3700_spi_transfer_one_fifo() doesn't call it if waiting for
> > "wfifo empty" or "xfer ready" has timed out.
> > Thus, this patch corrects error handling of them.
>
> The core shouldn't be waiting at all if the driver returned an error, we
> only wait if the return value was positive. Looking at the code it's
> not clear to me how we manage to end up waiting - it looks like the
> driver passes back the error correctly and the core looks like it does
> the right thing. Have you seen hangs in operation?
Yes, and I could avoid hanging by this patch. But I also understand that
your point is correct. Probably I'm misunderstanding the cause of the hang.
I will investigate a little more.

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