[PATCH] virtio: rng: gracefully handle 0 byte returns

[Tom Rini]

On Tue, Nov 07, 2023 at 04:09:00PM +0000, Andre Przywara wrote:

> According to the virtio v1.x "entropy device" specification, a virtio-rng
> device is supposed to always return at least one byte of entropy.
> However the virtio v0.9 spec does not mention such a requirement.
> 
> The Arm Fixed Virtual Platform (FVP) implementation of virtio-rng always
> returns 8 bytes less of entropy than requested. If 8 bytes or less are
> requested, it will return 0 bytes.
> This behaviour makes U-Boot's virtio_rng_read() implementation go into an
> endless loop, hanging the system.
> 
> Work around this problem by always requesting 8 bytes more than needed,
> but only if a previous call to virtqueue_get_buf() returned 0 bytes.
> 
> This should never trigger on a v1.x spec compliant implementation, but
> fixes the hang on the Arm FVP.
> 
> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
> Reported-by: Peter Hoyes <peter.hoyes at arm.com>

Applied to u-boot/master, thanks!

-- 
Tom
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