SPI lock-up with zero-length transfers

Nicolas Saenz Julienne nsaenzjulienne at suse.de
Thu Jan 28 09:33:29 EST 2021

On Thu, 2021-01-28 at 14:26 +0000, Phil Elwell wrote:
> Hi,
> Commit [1] - an optimisation of the PIO transfers loops of spi-bcm2835
> - causes lockups if a zero-length transfer is attempted. The commit
> message says that "[t]he blind and counted loops are always called
> with nonzero count", which is technically true but ignores the fact
> that count can be reduced to zero before entering the loop if tfr->len
> is zero.
> A workaround has been added in the raspberrypi/linux repo that
> explicitly checks for zero-length transfers in
> bcm2835_spi_transfer_one, but perhaps it would be better to catch this
> degenerate case in the common framework code - I'm not an SPI expert.

Me neither to be honest, but I'll have a look at it. Thanks for the heads-up.


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