Re: [PATCH 0/1] transport-mmio: Add optional reset completion polling

On Wed, Feb 04, 2026 at 12:50:21PM +0100, Peter Hilber wrote:
> Let devices using the MMIO transport avoid stalling the driver (virtual)
> CPU during device reset, which requires introducing a new MMIO transport
> version. This proposal is similar to [1], but simpler.
> 
> If the device reset includes terminating device activity which may
> interfere with the driver, the reset should always have completed by the
> time the driver considers the reset complete. After device reset, the
> driver may free previously exposed buffers. Per the current MMIO transport
> specification, the device must hence complete the reset during the write of
> 0 to the Status register. If terminating the device activity takes long,
> the (virtual) CPU doing this write to the Status register must be stalled
> for extended time, which may violate real-time requirements (including
> those for hypervisor trap-and-emulate).
> 
> Address this by introducing a new MMIO transport version, v3, where the
> driver must poll for reset completion, and, hence, the device reset does
> not have to finish during the write of 0 to the Status register. Polling
> for an operation to finish is a pattern also used for the PCI transport
> device reset, device suspend, and MMIO transport QueueReset writes.

This patch has been pending for one month without replies. Any review or
feedback would be very welcome.

Best regards,

Peter

> 
> Unlike [1], this proposal does not require a reset-in-progress status bit.
> Unlike [1], devices cannot indicate that the reset failed, which appears
> unneeded.
> 
> This proposal has been verified with proof-of-concept implementations for
> the Linux kernel and EDK2 OVMF Virtio drivers (supporting v2 and v3), and
> for the QEMU Virtio devices.
> 
> [1] https://www.mail-archive.com/[email protected]/msg07677.html
> 
> Signed-off-by: Peter Hilber <[email protected]>
> 
> 
> Peter Hilber (1):
>   transport-mmio: Add v3, which polls for reset completion
> 
>  transport-mmio.tex | 26 +++++++++++++++++++++++---
>  1 file changed, 23 insertions(+), 3 deletions(-)
> 
> 
> base-commit: 5187698cc6f40fd2f2a714ca3faa6e998c5fc231
> -- 
> 2.43.0
>