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R. Silva" , Marek Szyprowski , Robin Murphy , Mark Brown , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Frank Li , Peng Fan , Sascha Hauer , linux-remoteproc@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, virtualization@lists.linux.dev, imx@lists.linux.dev, iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH RFC 05/12] remoteproc: always report VIRTIO_F_VERSION_1 feature Message-ID: References: <20260916-remoteproc_virtio_map-v1-0-dac8c5eb4aa9@valla.it> <20260916-remoteproc_virtio_map-v1-5-dac8c5eb4aa9@valla.it> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Sep 22, 2026 at 08:32:15AM +0200, Francesco Valla wrote: > On Mon, Sep 21, 2026 at 09:47:54AM -0600, Mathieu Poirier wrote: > > 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 > > > --- > > > 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? > > > > Bits > 31 gets silently dropped because rsc->gfeatures is a u32; this > was inserted to explicitly drop the flag that has been inserted before > and avoid the "silently". It has no real funtional impact and can be > safely dropped. > We have come to the same conclusion. > > > return 0; > > > } > > > > > > -- > > > 2.55.0 > > >