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firmware: arm_scmi: Mark VirtIO ready before registering scmi_virtio_driver

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After commit 20bda12a0e (“firmware: arm_scmi: Make VirtIO transport a
standalone driver”), the VirtIO transport probes independently. During
scmi_virtio_probe, scmi_probe() is called, which intune invokes
scmi_protocol_acquire() that sends a message over the virtqueue and
waits for a reply.

Previously, DRIVER_OK was only set after scmi_vio_probe, in the core
virtio via virtio_dev_probe(). According to the Virtio spec (3.1 Device
Initialization):
  |  The driver MUST NOT send any buffer available notifications to the
  |  device before setting DRIVER_OK.

Some type-1 hypervisors block available-buffer notifications until the
driver is marked OK. In such cases, scmi_vio_probe stalls in
scmi_wait_for_reply(), and the probe never completes.

Resolve this by setting DRIVER_OK immediately after the device-specific
setup, so scmi_probe() can safely send notifications.

Note after splitting the transports into modules, the probe sequence
changed a bit. We can no longer rely on virtio_device_ready() being
called by the core in virtio_dev_probe(), because scmi_vio_probe()
doesn’t complete until the core SCMI stack runs scmi_probe(), which
immediately issues the initial BASE protocol exchanges.

Fixes: 20bda12a0e ("firmware: arm_scmi: Make VirtIO transport a standalone driver")
Signed-off-by: Junnan Wu <junnan01.wu@samsung.com>
Message-Id: <20250812075343.3201365-1-junnan01.wu@samsung.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
This commit is contained in:
Junnan Wu 2025-08-12 15:53:43 +08:00 committed by Sudeep Holla
parent 224dcf2968
commit e8faa8a466
1 changed files with 3 additions and 0 deletions
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3
drivers/firmware/arm_scmi/transports/virtio.c
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@ -871,6 +871,9 @@ static int scmi_vio_probe(struct virtio_device *vdev)
/* Ensure initialized scmi_vdev is visible */
smp_store_mb(scmi_vdev, vdev);
/* Set device ready */
virtio_device_ready(vdev);
ret = platform_driver_register(&scmi_virtio_driver);
if (ret) {
vdev->priv = NULL;