[PATCH] virtio: mmio: Return error codes on probe failures

[PATCH] virtio: mmio: Return error codes on probe failures

[Kuan-Wei Chiu]

Currently, virtio_mmio_probe() returns 0 when it encounters an invalid
magic value, an unsupported version, or a dummy device (ID 0). In
U-Boot's driver model, returning 0 indicates a successful probe. This
causes the system to incorrectly register and activate invalid or
placeholder devices, potentially leading to undefined behavior or
crashes later on.

Update the probe function to return appropriate error codes (-ENODEV
for invalid magic values and dummy devices, and -ENXIO for unsupported
versions). This fix correctly instructs the DM to abort the binding
process.

Fixes: fdc4aca89ecb ("virtio: Add virtio over mmio transport driver")
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
 drivers/virtio/virtio_mmio.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 1cd737aca24..62afe609ec0 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -354,7 +354,7 @@ static int virtio_mmio_probe(struct udevice *udev)
 	magic = readl(priv->base + VIRTIO_MMIO_MAGIC_VALUE);
 	if (magic != ('v' | 'i' << 8 | 'r' << 16 | 't' << 24)) {
 		debug("(%s): wrong magic value 0x%08x!\n", udev->name, magic);
-		return 0;
+		return -ENODEV;
 	}
 
 	/* Check device version */
@@ -362,7 +362,7 @@ static int virtio_mmio_probe(struct udevice *udev)
 	if (priv->version < 1 || priv->version > 2) {
 		debug("(%s): version %d not supported!\n",
 		      udev->name, priv->version);
-		return 0;
+		return -ENXIO;
 	}
 
 	/* Check device ID */
@@ -372,7 +372,7 @@ static int virtio_mmio_probe(struct udevice *udev)
 		 * virtio-mmio device with an ID 0 is a (dummy) placeholder
 		 * with no function. End probing now with no error reported.
 		 */
-		return 0;
+		return -ENODEV;
 	}
 	uc_priv->vendor = readl(priv->base + VIRTIO_MMIO_VENDOR_ID);
 
-- 
2.53.0.1213.gd9a14994de-goog

Re: [PATCH] virtio: mmio: Return error codes on probe failures

[Daniel Palmer]

Hi Kuan-Wei,

On Tue, 7 Apr 2026 at 18:49, Kuan-Wei Chiu <visitorckw@gmail.com> wrote:
>
> Currently, virtio_mmio_probe() returns 0 when it encounters an invalid
> magic value, an unsupported version, or a dummy device (ID 0). In
> U-Boot's driver model, returning 0 indicates a successful probe. This
> causes the system to incorrectly register and activate invalid or
> placeholder devices, potentially leading to undefined behavior or
> crashes later on.
>
> Update the probe function to return appropriate error codes (-ENODEV
> for invalid magic values and dummy devices, and -ENXIO for unsupported
> versions). This fix correctly instructs the DM to abort the binding
> process.
>
> Fixes: fdc4aca89ecb ("virtio: Add virtio over mmio transport driver")
> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> ---
>  drivers/virtio/virtio_mmio.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index 1cd737aca24..62afe609ec0 100644
> --- a/drivers/virtio/virtio_mmio.c
> +++ b/drivers/virtio/virtio_mmio.c
> @@ -354,7 +354,7 @@ static int virtio_mmio_probe(struct udevice *udev)
>         magic = readl(priv->base + VIRTIO_MMIO_MAGIC_VALUE);
>         if (magic != ('v' | 'i' << 8 | 'r' << 16 | 't' << 24)) {
>                 debug("(%s): wrong magic value 0x%08x!\n", udev->name, magic);
> -               return 0;
> +               return -ENODEV;
>         }
>
>         /* Check device version */
> @@ -362,7 +362,7 @@ static int virtio_mmio_probe(struct udevice *udev)
>         if (priv->version < 1 || priv->version > 2) {
>                 debug("(%s): version %d not supported!\n",
>                       udev->name, priv->version);
> -               return 0;
> +               return -ENXIO;
>         }
>
>         /* Check device ID */
> @@ -372,7 +372,7 @@ static int virtio_mmio_probe(struct udevice *udev)
>                  * virtio-mmio device with an ID 0 is a (dummy) placeholder
>                  * with no function. End probing now with no error reported.
>                  */
> -               return 0;
> +               return -ENODEV;
>         }
>         uc_priv->vendor = readl(priv->base + VIRTIO_MMIO_VENDOR_ID);
>
> --
> 2.53.0.1213.gd9a14994de-goog
>

I'm surprised I didn't notice this when working out the endian issues on m68k.
I have build/boot tested on m68k and the change looks correct to me.

Since I'm not the maintainer for this thing I guess:

Acked-by: Daniel Palmer <daniel@thingy.jp>