i2c: virtio: Add support for zero-length requests

The virtio specification received a new mandatory feature
(VIRTIO_I2C_F_ZERO_LENGTH_REQUEST) for zero length requests. Fail if the
feature isn't offered by the device.

For each read-request, set the VIRTIO_I2C_FLAGS_M_RD flag, as required
by the VIRTIO_I2C_F_ZERO_LENGTH_REQUEST feature.

This allows us to support zero length requests, like SMBUS Quick, where
the buffer need not be sent anymore.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lore.kernel.org/r/7c58868cd26d2fc4bd82d0d8b0dfb55636380110.1634808714.git.viresh.kumar@linaro.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jie Deng <jie.deng@intel.com> # once the spec is merged

diff --git a/drivers/i2c/busses/i2c-virtio.c b/drivers/i2c/busses/i2c-virtio.c
index f10a603..1ed4daa 100644 (file)
--- a/drivers/i2c/busses/i2c-virtio.c
+++ b/drivers/i2c/busses/i2c-virtio.c
@@ -63,34 +63,32 @@ static int virtio_i2c_prepare_reqs(struct virtqueue *vq,
                int outcnt = 0, incnt = 0;
 
                /*
-                * We don't support 0 length messages and so filter out
-                * 0 length transfers by using i2c_adapter_quirks.
-                */
-               if (!msgs[i].len)
-                       break;
-
-               /*
                 * Only 7-bit mode supported for this moment. For the address
                 * format, Please check the Virtio I2C Specification.
                 */
                reqs[i].out_hdr.addr = cpu_to_le16(msgs[i].addr << 1);
 
+               if (msgs[i].flags & I2C_M_RD)
+                       reqs[i].out_hdr.flags |= cpu_to_le32(VIRTIO_I2C_FLAGS_M_RD);
+
                if (i != num - 1)
-                       reqs[i].out_hdr.flags = cpu_to_le32(VIRTIO_I2C_FLAGS_FAIL_NEXT);
+                       reqs[i].out_hdr.flags |= cpu_to_le32(VIRTIO_I2C_FLAGS_FAIL_NEXT);
 
                sg_init_one(&out_hdr, &reqs[i].out_hdr, sizeof(reqs[i].out_hdr));
                sgs[outcnt++] = &out_hdr;
 
-               reqs[i].buf = i2c_get_dma_safe_msg_buf(&msgs[i], 1);
-               if (!reqs[i].buf)
-                       break;
+               if (msgs[i].len) {
+                       reqs[i].buf = i2c_get_dma_safe_msg_buf(&msgs[i], 1);
+                       if (!reqs[i].buf)
+                               break;
 
-               sg_init_one(&msg_buf, reqs[i].buf, msgs[i].len);
+                       sg_init_one(&msg_buf, reqs[i].buf, msgs[i].len);
 
-               if (msgs[i].flags & I2C_M_RD)
-                       sgs[outcnt + incnt++] = &msg_buf;
-               else
-                       sgs[outcnt++] = &msg_buf;
+                       if (msgs[i].flags & I2C_M_RD)
+                               sgs[outcnt + incnt++] = &msg_buf;
+                       else
+                               sgs[outcnt++] = &msg_buf;
+               }
 
                sg_init_one(&in_hdr, &reqs[i].in_hdr, sizeof(reqs[i].in_hdr));
                sgs[outcnt + incnt++] = &in_hdr;
@@ -191,7 +189,7 @@ static int virtio_i2c_setup_vqs(struct virtio_i2c *vi)
 
 static u32 virtio_i2c_func(struct i2c_adapter *adap)
 {
-       return I2C_FUNC_I2C | (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK);
+       return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
 }
 
 static struct i2c_algorithm virtio_algorithm = {
@@ -199,15 +197,16 @@ static struct i2c_algorithm virtio_algorithm = {
        .functionality = virtio_i2c_func,
 };
 
-static const struct i2c_adapter_quirks virtio_i2c_quirks = {
-       .flags = I2C_AQ_NO_ZERO_LEN,
-};
-
 static int virtio_i2c_probe(struct virtio_device *vdev)
 {
        struct virtio_i2c *vi;
        int ret;
 
+       if (!virtio_has_feature(vdev, VIRTIO_I2C_F_ZERO_LENGTH_REQUEST)) {
+               dev_err(&vdev->dev, "Zero-length request feature is mandatory\n");
+               return -EINVAL;
+       }
+
        vi = devm_kzalloc(&vdev->dev, sizeof(*vi), GFP_KERNEL);
        if (!vi)
                return -ENOMEM;
@@ -225,7 +224,6 @@ static int virtio_i2c_probe(struct virtio_device *vdev)
        snprintf(vi->adap.name, sizeof(vi->adap.name),
                 "i2c_virtio at virtio bus %d", vdev->index);
        vi->adap.algo = &virtio_algorithm;
-       vi->adap.quirks = &virtio_i2c_quirks;
        vi->adap.dev.parent = &vdev->dev;
        vi->adap.dev.of_node = vdev->dev.of_node;
        i2c_set_adapdata(&vi->adap, vi);
@@ -270,11 +268,17 @@ static int virtio_i2c_restore(struct virtio_device *vdev)
 }
 #endif
 
+static const unsigned int features[] = {
+       VIRTIO_I2C_F_ZERO_LENGTH_REQUEST,
+};
+
 static struct virtio_driver virtio_i2c_driver = {
-       .id_table       = id_table,
-       .probe          = virtio_i2c_probe,
-       .remove         = virtio_i2c_remove,
-       .driver = {
+       .feature_table          = features,
+       .feature_table_size     = ARRAY_SIZE(features),
+       .id_table               = id_table,
+       .probe                  = virtio_i2c_probe,
+       .remove                 = virtio_i2c_remove,
+       .driver                 = {
                .name   = "i2c_virtio",
        },
 #ifdef CONFIG_PM_SLEEP

diff --git a/include/uapi/linux/virtio_i2c.h b/include/uapi/linux/virtio_i2c.h
index 7c6a6fc..acf3b60 100644 (file)
--- a/include/uapi/linux/virtio_i2c.h
+++ b/include/uapi/linux/virtio_i2c.h
@@ -11,9 +11,15 @@
 #include <linux/const.h>
 #include <linux/types.h>
 
+/* Virtio I2C Feature bits */
+#define VIRTIO_I2C_F_ZERO_LENGTH_REQUEST       0
+
 /* The bit 0 of the @virtio_i2c_out_hdr.@flags, used to group the requests */
 #define VIRTIO_I2C_FLAGS_FAIL_NEXT     _BITUL(0)
 
+/* The bit 1 of the @virtio_i2c_out_hdr.@flags, used to mark a buffer as read */
+#define VIRTIO_I2C_FLAGS_M_RD          _BITUL(1)
+
 /**
  * struct virtio_i2c_out_hdr - the virtio I2C message OUT header
  * @addr: the controlled device address