[RFC PATCH v2 7/7] vringh: IOMEM support

[Shunsuke Mie]

This patch introduces the new memory accessor for vringh. It is able to
use vringh to virtio rings located on iomemory region.

Signed-off-by: Shunsuke Mie <mie@xxxxxxxxxx>
---
 drivers/vhost/Kconfig  |  6 ++++
 drivers/vhost/vringh.c | 76 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/vringh.h |  8 +++++
 3 files changed, 90 insertions(+)

diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 587fbae06182..a79a4efbc817 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -6,6 +6,12 @@ config VHOST_IOTLB
 	  This option is selected by any driver which needs to support
 	  an IOMMU in software.
 
+config VHOST_IOMEM
+	tristate
+	select VHOST_RING
+	help
+	  Generic IOMEM implementation for vhost and vringh.
+
 config VHOST_RING
 	tristate
 	select VHOST_IOTLB
diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
index 46fb315483ed..e3d9c7281ad0 100644
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c
@@ -18,6 +18,9 @@
 #include <linux/highmem.h>
 #include <linux/vhost_iotlb.h>
 #endif
+#if IS_REACHABLE(CONFIG_VHOST_IOMEM)
+#include <linux/io.h>
+#endif
 #include <uapi/linux/virtio_config.h>
 
 static __printf(1,2) __cold void vringh_bad(const char *fmt, ...)
@@ -1165,4 +1168,77 @@ EXPORT_SYMBOL(vringh_set_iotlb);
 
 #endif
 
+#if IS_REACHABLE(CONFIG_VHOST_IOMEM)
+
+/* io-memory space access helpers. */
+static int getu16_iomem(const struct vringh *vrh, u16 *val, const __virtio16 *p)
+{
+	*val = vringh16_to_cpu(vrh, ioread16(p));
+	return 0;
+}
+
+static int putu16_iomem(const struct vringh *vrh, __virtio16 *p, u16 val)
+{
+	iowrite16(cpu_to_vringh16(vrh, val), p);
+	return 0;
+}
+
+static int copydesc_iomem(const struct vringh *vrh, void *dst, const void *src,
+			  size_t len)
+{
+	memcpy_fromio(dst, src, len);
+	return 0;
+}
+
+static int putused_iomem(const struct vringh *vrh, struct vring_used_elem *dst,
+			 const struct vring_used_elem *src, unsigned int num)
+{
+	memcpy_toio(dst, src, num * sizeof(*dst));
+	return 0;
+}
+
+static int xfer_from_iomem(const struct vringh *vrh, void *src, void *dst,
+			   size_t len)
+{
+	memcpy_fromio(dst, src, len);
+	return 0;
+}
+
+static int xfer_to_iomem(const struct vringh *vrh, void *dst, void *src,
+			 size_t len)
+{
+	memcpy_toio(dst, src, len);
+	return 0;
+}
+
+static struct vringh_ops iomem_vringh_ops = {
+	.getu16 = getu16_iomem,
+	.putu16 = putu16_iomem,
+	.xfer_from = xfer_from_iomem,
+	.xfer_to = xfer_to_iomem,
+	.putused = putused_iomem,
+	.copydesc = copydesc_iomem,
+	.range_check = no_range_check,
+	.getrange = NULL,
+};
+
+int vringh_init_iomem(struct vringh *vrh, u64 features, unsigned int num,
+		      bool weak_barriers, gfp_t gfp, struct vring_desc *desc,
+		      struct vring_avail *avail, struct vring_used *used)
+{
+	int err;
+
+	err = __vringh_init(vrh, features, num, weak_barriers, gfp, desc, avail,
+			    used);
+	if (err)
+		return err;
+
+	memcpy(&vrh->ops, &iomem_vringh_ops, sizeof(iomem_vringh_ops));
+
+	return 0;
+}
+EXPORT_SYMBOL(vringh_init_iomem);
+
+#endif
+
 MODULE_LICENSE("GPL");
diff --git a/include/linux/vringh.h b/include/linux/vringh.h
index 89c73605c85f..420c2d0ed398 100644
--- a/include/linux/vringh.h
+++ b/include/linux/vringh.h
@@ -265,4 +265,12 @@ int vringh_init_iotlb(struct vringh *vrh, u64 features,
 
 #endif /* CONFIG_VHOST_IOTLB */
 
+#if IS_REACHABLE(CONFIG_VHOST_IOMEM)
+
+int vringh_init_iomem(struct vringh *vrh, u64 features, unsigned int num,
+		      bool weak_barriers, gfp_t gfp, struct vring_desc *desc,
+		      struct vring_avail *avail, struct vring_used *used);
+
+#endif /* CONFIG_VHOST_IOMEM */
+
 #endif /* _LINUX_VRINGH_H */
-- 
2.25.1