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Tsirkin" To: Andrew Stellman Cc: Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , virtualization@lists.linux.dev Subject: Re: [PATCH 1/4] virtio-mmio: wait for status readback after reset Message-ID: <20260407122409-mutt-send-email-mst@kernel.org> References: <20260407123904.6390-1-astellman@stellman-greene.com> <20260407123904.6390-2-astellman@stellman-greene.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20260407123904.6390-2-astellman@stellman-greene.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: AxmBMs_ufHIxQ4OFDVhz-D67j5ef4WNRCo53EzfBWhk_1775579086 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Apr 07, 2026 at 08:39:01AM -0400, Andrew Stellman wrote: > The virtio specification requires that after writing 0 to the status > register, the driver must wait until the device has actually completed > the reset (status reads back as 0) before proceeding. It does? But where? I see: Reading from this register returns the current device status flags. Writing non-zero values to this register sets the status flags, indicating the OS/driver progress. Writing zero (0x0) to this register triggers a device reset. The device sets \field{QueuePFN} to zero (0x0) for all queues in the device. > vm_reset() writes > 0 but returns immediately without confirming the device has reset. > > Add a poll loop matching the pattern already used in virtio-pci's > vp_reset(), which calls msleep(1) in a loop until the status register > reads 0. > > Signed-off-by: Andrew Stellman > --- > drivers/virtio/virtio_mmio.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c > index 595c227..a477977 100644 > --- a/drivers/virtio/virtio_mmio.c > +++ b/drivers/virtio/virtio_mmio.c > @@ -56,6 +56,7 @@ > > #include > #include > +#include > #include > #include > #include > @@ -254,6 +255,8 @@ static void vm_reset(struct virtio_device *vdev) > > /* 0 status means a reset. */ > writel(0, vm_dev->base + VIRTIO_MMIO_STATUS); > + while (readl(vm_dev->base + VIRTIO_MMIO_STATUS)) > + msleep(1); > } > > > -- > 2.34.1