linux-kernel - [PATCH] firmware: arm_scmi: Set device ready before register scmi_virtio

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Message-Id: <20250812075343.3201365-1-junnan01.wu@samsung.com>
Date: Tue, 12 Aug 2025 15:53:43 +0800
From: Junnan Wu <junnan01.wu@...sung.com>
To: sudeep.holla@....com, cristian.marussi@....com
Cc: florian.fainelli@...adcom.com, arm-scmi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	lei19.wang@...sung.com, q1.huang@...sung.com, Junnan Wu
	<junnan01.wu@...sung.com>
Subject: [PATCH] firmware: arm_scmi: Set device ready before register
 scmi_virtio_driver

Fix irregularities in scmi driver probe.

After 'commit 20bda12a0ea0 ("firmware: arm_scmi: Make VirtIO transport a standalone driver")'
making SCMI VirtIO transport a standalone driver,
`scmi_virtio_probe` will follow `scmi_vio_probe`,
and during `scmi_virtio_probe`, it will do `scmi_probe` which will invoke
function `scmi_protocol_acquire(handle, SCMI_PROTOCOL_BASE)`,
and this function will send message via virtqueue and wait device's reply

Before this patch, only after `scmi_vio_probe`,
frontend will mark device DRIVER_OK by function `virtio_dev_probe`
in 'drivers/virtio/virtio.c' itself.

Accroding to chapter '3.1 Device Initialization' in virtio-spec,
```
The driver MUST NOT send any buffer available notifications
to the device before setting DRIVER_OK.
```

In some type1-hypervisor, available buffer notifications
will be intercepted until virtio driver is okay. In this case,
`scmi_vio_probe` will be blocked at `scmi_wait_for_reply`
and probe can never complete.

Therefore, the operation to set DRIVER_OK must follow
perform device-specific setup immediately,
then available buffer notifications can be sent in function `scmi_probe`.

Fixes: 20bda12a0ea0 ("firmware: arm_scmi: Make VirtIO transport a standalone driver")
Signed-off-by: Junnan Wu <junnan01.wu@...sung.com>
---
 drivers/firmware/arm_scmi/transports/virtio.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/firmware/arm_scmi/transports/virtio.c b/drivers/firmware/arm_scmi/transports/virtio.c
index cb934db9b2b4..326c4a93e44b 100644
--- a/drivers/firmware/arm_scmi/transports/virtio.c
+++ b/drivers/firmware/arm_scmi/transports/virtio.c
@@ -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;
-- 
2.34.1