From c45a6816c19dee67b8f725e6646d428901a6dc24 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Fri, 2 May 2008 21:50:50 -0500 Subject: virtio: explicit advertisement of driver features A recent proposed feature addition to the virtio block driver revealed some flaws in the API: in particular, we assume that feature negotiation is complete once a driver's probe function returns. There is nothing in the API to require this, however, and even I didn't notice when it was violated. So instead, we require the driver to specify what features it supports in a table, we can then move the feature negotiation into the virtio core. The intersection of device and driver features are presented in a new 'features' bitmap in the struct virtio_device. Note that this highlights the difference between Linux unsigned-long bitmaps where each unsigned long is in native endian, and a straight-forward little-endian array of bytes. Drivers can still remove feature bits in their probe routine if they really have to. API changes: - dev->config->feature() no longer gets and acks a feature. - drivers should advertise their features in the 'feature_table' field - use virtio_has_feature() for extra sanity when checking feature bits Signed-off-by: Rusty Russell --- drivers/virtio/virtio_pci.c | 30 +++++++++++++++--------------- 1 file changed, 15 insertions(+), 15 deletions(-) (limited to 'drivers/virtio/virtio_pci.c') diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c index de102a614e9..27e9fc9117c 100644 --- a/drivers/virtio/virtio_pci.c +++ b/drivers/virtio/virtio_pci.c @@ -87,23 +87,22 @@ static struct virtio_pci_device *to_vp_device(struct virtio_device *vdev) return container_of(vdev, struct virtio_pci_device, vdev); } -/* virtio config->feature() implementation */ -static bool vp_feature(struct virtio_device *vdev, unsigned bit) +/* virtio config->get_features() implementation */ +static u32 vp_get_features(struct virtio_device *vdev) +{ + struct virtio_pci_device *vp_dev = to_vp_device(vdev); + + /* When someone needs more than 32 feature bits, we'll need to + * steal a bit to indicate that the rest are somewhere else. */ + return ioread32(vp_dev->ioaddr + VIRTIO_PCI_HOST_FEATURES); +} + +/* virtio config->set_features() implementation */ +static void vp_set_features(struct virtio_device *vdev, u32 features) { struct virtio_pci_device *vp_dev = to_vp_device(vdev); - u32 mask; - - /* Since this function is supposed to have the side effect of - * enabling a queried feature, we simulate that by doing a read - * from the host feature bitmask and then writing to the guest - * feature bitmask */ - mask = ioread32(vp_dev->ioaddr + VIRTIO_PCI_HOST_FEATURES); - if (mask & (1 << bit)) { - mask |= (1 << bit); - iowrite32(mask, vp_dev->ioaddr + VIRTIO_PCI_GUEST_FEATURES); - } - return !!(mask & (1 << bit)); + iowrite32(features, vp_dev->ioaddr + VIRTIO_PCI_GUEST_FEATURES); } /* virtio config->get() implementation */ @@ -293,7 +292,6 @@ static void vp_del_vq(struct virtqueue *vq) } static struct virtio_config_ops virtio_pci_config_ops = { - .feature = vp_feature, .get = vp_get, .set = vp_set, .get_status = vp_get_status, @@ -301,6 +299,8 @@ static struct virtio_config_ops virtio_pci_config_ops = { .reset = vp_reset, .find_vq = vp_find_vq, .del_vq = vp_del_vq, + .get_features = vp_get_features, + .set_features = vp_set_features, }; /* the PCI probing function */ -- cgit