On Fri, Sep 27, 2024 at 12:08:34PM +0800, Jason Wang wrote: > On Thu, Sep 26, 2024 at 2:09 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > > On Thu, Sep 26, 2024 at 11:21:25AM +0800, Jason Wang wrote: > > > On Thu, Sep 26, 2024 at 10:27 AM Jianguo Sun <quic_jianguos@xxxxxxxxxxx> wrote: > > > > > > > > We write 0 to device_status to initiate reset of a virtio-mmio device. > > > > The reset operation itself may or may not be completed by the time > > > > write instruction completes. Add polling device_status to return > > > > 0 to ensure reset completion before reinitializing the device. > > > > > > > > Change-Id: If15d11d090dfd0d4972ad35f49af03e076872413 > > > > Signed-off-by: Jianguo Sun <quic_jianguos@xxxxxxxxxxx> > > > > Signed-off-by: Sreenad Menon <quic_sreemeno@xxxxxxxxxxx> > > > > Signed-off-by: Anant Goel <quic_anantg@xxxxxxxxxxx> > > > > --- > > > > drivers/virtio/virtio_mmio.c | 6 ++++++ > > > > 1 file changed, 6 insertions(+) > > > > > > > > diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c > > > > index 90e784e7b721..cf1a4a3dd35d 100644 > > > > --- a/drivers/virtio/virtio_mmio.c > > > > +++ b/drivers/virtio/virtio_mmio.c > > > > @@ -70,6 +70,7 @@ > > > > #include <linux/virtio_config.h> > > > > #include <uapi/linux/virtio_mmio.h> > > > > #include <linux/virtio_ring.h> > > > > +#include <linux/delay.h> > > > > > > > > > > > > > > > > @@ -269,6 +270,11 @@ static void vm_reset(struct virtio_device *vdev) > > > > > > > > /* 0 status means a reset. */ > > > > writel(0, vm_dev->base + VIRTIO_MMIO_STATUS); > > > > + /* After writing 0 to device_status, the driver MUST wait for a read of > > > > + * device_status to return 0 before reinitializing the device. > > > > + */ > > > > > > Is this copied from the spec? I can only see a similar description in > > > the PCI but not MMIO part. > > > > Not in spec. We can add something like this in spec, but it > > can not be a MUST, has to be a SHOULD. > > > > > > + while (readl(vm_dev->base + VIRTIO_MMIO_STATUS)) > > > > + msleep(1); > > > > > > Again, we probably need a feature bit to unbreak existing MMIO devices? > > > > > > THanks > > > > We can do this unconditionally since legacy devices return 0 > > immediately, > > The problem is that we can't audit all legacy device implementations. > Current driver still works if a device doesn't reset status to 0. These would be out of spec though, would they not? The reset value for the register is 0, and it is R/W. > > feature negotiation happens after reset, won't be useful > > here. > > Right, as said in another thread, it could be mmio specific flag or version. > > Thanks > > > > > > > > > } > > > > > > > > > > > > -- > > > > 2.17.1 > > > > > >
