Re: [PATCH RFC 05/12] remoteproc: always report VIRTIO_F_VERSION_1 feature

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Wed, Sep 16, 2026 at 11:10:50PM +0200, Francesco Valla wrote:
> There is currently no way to report the VIRTIO_F_VERSION_1 using the
> resource table alone, as the per-vdev feature array is limited to 32
> bits.
> 
> Considering that the VirtIO 1.0 specification is now ~10 years old,
> always report the VIRTIO_F_VERSION_1 feature, as some drivers depend on
> it.
> 
> Signed-off-by: Francesco Valla <francesco@valla.it>
> ---
>  drivers/remoteproc/remoteproc_virtio.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/remoteproc/remoteproc_virtio.c b/drivers/remoteproc/remoteproc_virtio.c
> index 74e0da970f1d..cfd66d9d1c9e 100644
> --- a/drivers/remoteproc/remoteproc_virtio.c
> +++ b/drivers/remoteproc/remoteproc_virtio.c
> @@ -249,7 +249,7 @@ static u64 rproc_virtio_get_features(struct virtio_device *vdev)
>  
>  	rsc = (void *)rvdev->rproc->table_ptr + rvdev->rsc_offset;
>  
> -	return rsc->dfeatures;
> +	return rsc->dfeatures | (1ULL << VIRTIO_F_VERSION_1);

I understand this.

>  }
>  
>  static void rproc_transport_features(struct virtio_device *vdev)
> @@ -275,14 +275,16 @@ static int rproc_virtio_finalize_features(struct virtio_device *vdev)
>  	/* Give virtio_rproc a chance to accept features. */
>  	rproc_transport_features(vdev);
>  
> -	/* Make sure we don't have any features > 32 bits! */
> -	BUG_ON((u32)vdev->features != vdev->features);
> +	/* Make sure we don't have any features > 32 bits except VIRTIO_F_VERSION_1 */
> +	if (WARN_ON_ONCE((u32)vdev->features !=
> +			 (vdev->features & ~(1ULL << VIRTIO_F_VERSION_1))))
> +		return -1;

And this.

>  
>  	/*
>  	 * Remember the finalized features of our vdev, and provide it
>  	 * to the remote processor once it is powered on.
>  	 */
> -	rsc->gfeatures = vdev->features;
> +	rsc->gfeatures = vdev->features & ~(1ULL << VIRTIO_F_VERSION_1);
>  

But I'm having trouble with this one.  

First bit 32 of vdev->features gets cleared and then bit 0 to 31 are assigned to
rsc->gfeatures.  Why bother with clearing bit 32?

>  	return 0;
>  }
> 
> -- 
> 2.55.0
>