On Fri, Apr 29 2022, 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) 0,0 -> queue reset is ongoing > conflicts with #a, because queue is still enabled in device > whose reset is in progress. > External entity has no knowledge if VQ is undergoing reset or > VQ is never enabled. > e) 0,1 -> queue reset is completed (conflicts with #a initial value) > > 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. > > Additionally, external entity that may have to manage a virtio device > cannot distinguish between #a and #d, whether a VQ is not yet enabled > or it is in use and undergoing a reset. > > 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") > Reviewed-by: Jason Wang <jasow...@redhat.com> > Reviewed-by: Xuan Zhuo <xuanz...@linux.alibaba.com> > Signed-off-by: Parav Pandit <pa...@nvidia.com>
LGTM now. --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org