From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Parav Pandit Subject: [PATCH v2] virtio: Improve queue_reset polarity to match to default reset state Date: Wed, 27 Apr 2022 13:25:59 +0300 Message-ID: <20220427102559.305669-1-parav@nvidia.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain To: virtio-dev@lists.oasis-open.org, xuanzhuo@linux.alibaba.com, jasowang@redhat.com, mst@redhat.com, cohuck@redhat.com Cc: stefanha@redhat.com, Parav Pandit List-ID: Currently when driver initiates a queue reset, device is expected to communicate reset status to the driver by changing the value of the queue_reset register twice. First to return value other than 1 when reset is ongoing, later to return 1 when queue reset is completed. However initially during the device reset time the queue reset value is zero. queue_reset changes the value of the register to a different value on reset completion. Yet another time queue_reset value is expected to change when queue_select is reprogrammed. For example in below flow, a created virtqueue, which is disabled by driver leaves the queue state as queue_enable =3D 0, queue_reset =3D 1. example flow: a) 0,0 -> device init time value b) 1,0 -> vq is enabled by driver and working c) 1,1 -> vq is enabled, driver initiated reset d) 1,0 -> vq is enabled, but device is busy doing the reset e) 0,1 -> vq reset is completed in the device and VQ is now disabled (conflict with initial queue reset state #a above) On next iteration, when queue_select selects the same VQ again, without enablement, device is confused to return 1 or 0 because it was reset once before via queue_reset register. This demands complex device implementation to understand what should be returned for a VQ that is reset using queue_reset register vs other means. Instead, it is better and efficient to maintain the same VQ state on the device when queue reset is completed. new proposed flow: q_enable, q_reset A) 0, 0 -> default, device init time B) 1, 0 -> driver has enabled vq C) 1, 1 -> driver started q reset D) 1, 1 -> q_reset stays 1 until device is busy resetting vq (device communicates that its working on resetting VQ, consistent with #C) E) 0, 0 -> q_reset by device is completed, q got disabled (consistent with device init time #A) Hence, this patch proposes a simple change to have reset register polarity to be same as that of initial reset value. Fixes: https://github.com/oasis-tcs/virtio-spec/issues/139 Fixes: 12998e738621 ("virtio: pci support virtqueue reset") Fixes: a4ce81a83780 ("virtio: mmio support virtqueue reset") Fixes: 3b5378d70a42 ("virtio: introduce virtqueue reset as basic facility") Signed-off-by: Parav Pandit --- changelog: v1->v2: - Fixed below comment from Xuan Zhuo - Fixed the configuration and register layout text to reflect the polarity v0->v1: - Fixed below comments from Michael - Removed example device side pseudo code for old and new polarity - Removed unwanted articles 'a' and 'the' - Dropped extra empty line --- content.tex | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-) diff --git a/content.tex b/content.tex index 060bdab..68b176b 100644 --- a/content.tex +++ b/content.tex @@ -1039,7 +1039,7 @@ \subsubsection{Common configuration structure layout}= \label{sec:Virtio Transport \field{queue_reset} after the virtqueue is enabled with \field{queue_enabl= e}. =20 The device MUST reset the queue when 1 is written to \field{queue_reset}, = and -present a 1 in \field{queue_reset} after the queue has been reset, until t= he +present 0 in \field{queue_reset} after the queue has been reset, until the driver re-enables the queue via \field{queue_enable} or the device is rese= t. The device MUST present consistent default values after queue reset. (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue= Reset}). @@ -1069,10 +1069,13 @@ \subsubsection{Common configuration structure layou= t}\label{sec:Virtio Transport The driver MUST NOT write a 0 to \field{queue_enable}. =20 If VIRTIO_F_RING_RESET has been negotiated, after the driver writes 1 to -\field{queue_reset} to reset the queue, it MUST verify that the queue -has been reset by reading back \field{queue_reset} and ensuring that it -is 1. The driver MAY re-enable the queue by writing a 1 to -\field{queue_enable} after ensuring that the other virtqueue fields have +\field{queue_reset} to reset the queue, driver MUST verify that the queue +has been reset by reading back \field{queue_reset} until device returns a = value of 0. +Device continue to report value of 1 for the \field{queue_reset} until dev= ice finishes +the queue reset request. When the device completes the queue reset, \field= {queue_reset} +and \field{queue_enable} set to zero, indicating +that specified queue is ready to be enabled again. The driver MAY re-enabl= e the queue by writing 1 to +\field{queue_enable} after ensuring that other virtqueue fields have been set up correctly. The driver MAY set driver-writeable queue configura= tion values to different values than those that were used before the queue rese= t. (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue= Reset}). @@ -2015,7 +2018,7 @@ \subsection{MMIO Device Register Layout}\label{sec:Vi= rtio Transport Options / Vi \field{QueueReset} after the virtqueue is enabled with \field{QueueReady}. =20 The device MUST reset the queue when 1 is written to \field{QueueReset}, a= nd -present a 1 in \field{QueueReset} after the queue has been reset, until th= e +present 0 in \field{QueueReset} after the queue has been reset, until the driver re-enables the queue via \field{QueueReady} or until the device is = reset. The device MUST present consistent default values after queue reset. (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue= Reset}). @@ -2063,10 +2066,13 @@ \subsection{MMIO Device Register Layout}\label{sec:= Virtio Transport Options / Vi it finishes handling an interrupt and MUST NOT set any of the undefined bi= ts in the value. =20 If VIRTIO_F_RING_RESET has been negotiated, after the driver writes 1 to -\field{QueueReset} to reset the queue, it MUST verify that the queue -has been reset by reading back \field{QueueReset} and ensuring that it -is 1. The driver MAY re-enable the queue by writing a 1 to -\field{QueueReady} after ensuring that the other virtqueue fields have +\field{QueueReset} to reset the queue, driver MUST verify that the queue +has been reset by reading back \field{QueueReset} until device returns a v= alue of 0. +Device continue to report value of 1 for the \field{QueueReset} until devi= ce finishes +the reset. When the device completes the queue reset, \field{QueueReset} a= nd +\field{QueueReady} set to zero, indicating that specified queue is ready t= o be +enabled again. The driver MAY re-enable the queue by writing 1 to +\field{QueueReady} after ensuring that other virtqueue fields have been set up correctly. The driver MAY set driver-writeable queue configura= tion values to different values than those that were used before the queue rese= t. (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue= Reset}). --=20 1.8.3.1