[PATCH] virtio-mmio: Specify wait needed in driver during reset

[Srivatsa Vaddagiri <svaddagi@qti.qualcomm.com>]

This is following up on the discussion we had earlier on MMIO reset behavior:

https://lists.oasis-open.org/archives/virtio-dev/202107/msg00012.html

Suggesting below change to spec to make it explicit what's expected in driver. If this is accepted, I will follow up with a patch to Linux driver.

===

Device reset is accomplished by writing 0 to Status register. Explicitly note

that a driver needs to wait on Status register read returning 0 before assuming that

device reset operation is complete.

   

Signed-off-by: Srivatsa Vaddagiri <svaddagi@qti.qualcomm.com>

diff --git a/content.tex b/content.tex

index 5c70a3c..7631be4 100644

--- a/content.tex

+++ b/content.tex

@@ -1985,6 +1985,10 @@ \subsubsection{Device Initialization}\label{sec:Virtio Transport Options / Virti

 and if its value is zero (0x0) MUST abort initialization and

 MUST NOT access any other register.

 

+After writing 0 to \field{Status}, the driver MUST wait for a read of

+\field{Status} to return 0 before proceeding with the remaining steps of

+initializing the device.

+

 Drivers not expecting shared memory MUST NOT use the shared

 memory registers.

 

---

Qualcomm Innovation Center, Inc. is submitting the attached "feedback" as a non-member to the virtio-dev mailing list for consideration and inclusion.