On Tue, 26 Apr 2022 03:06:57 +0300, Parav Pandit <pa...@nvidia.com> wrote: > 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 = 0, queue_reset = 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 <pa...@nvidia.com> > > --- > changelog: > v0->v1: > - 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..fc314ed 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_enable}. > > 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 the > +present 1 in \field{queue_reset} after the queue has been reset, until the
1 -> 0? > driver re-enables the queue via \field{queue_enable} or 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}). > @@ -1069,10 +1069,13 @@ \subsubsection{Common configuration structure > layout}\label{sec:Virtio Transport > The driver MUST NOT write a 0 to \field{queue_enable}. > > 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 > device 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-enable > 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 > configuration > values to different values than those that were used before the queue reset. > (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue > Reset}). > @@ -2015,7 +2018,7 @@ \subsection{MMIO Device Register > Layout}\label{sec:Virtio Transport Options / Vi > \field{QueueReset} after the virtqueue is enabled with \field{QueueReady}. > > The device MUST reset the queue when 1 is written to \field{QueueReset}, and > -present a 1 in \field{QueueReset} after the queue has been reset, until the > +present 1 in \field{QueueReset} after the queue has been reset, until the 1 -> 0? Thanks. > 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 bits > in the value. > > 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 > value of 0. > +Device continue to report value of 1 for the \field{QueueReset} until device > finishes > +the reset. When the device completes the queue reset, \field{QueueReset} and > +\field{QueueReady} set to zero, indicating that specified queue is ready to > 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 > configuration > values to different values than those that were used before the queue reset. > (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue > Reset}). > -- > 1.8.3.1 > --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org