Merge branch 'support-direct-read-from-region'

Jacob Keller says:

====================
support direct read from region

A long time ago when initially implementing devlink regions in ice I
proposed the ability to allow reading from a region without taking a
snapshot [1]. I eventually dropped this work from the original series due to
size. Then I eventually lost track of submitting this follow up.

This can be useful when interacting with some region that has some
definitive "contents" from which snapshots are made. For example the ice
driver has regions representing the contents of the device flash.

If userspace wants to read the contents today, it must first take a snapshot
and then read from that snapshot. This makes sense if you want to read a
large portion of data or you want to be sure reads are consistently from the
same recording of the flash.

However if user space only wants to read a small chunk, it must first
generate a snapshot of the entire contents, perform a read from the
snapshot, and then delete the snapshot after reading.

For such a use case, a direct read from the region makes more sense. This
can be achieved by allowing the devlink region read command to work without
a snapshot. Instead the portion to be read can be forwarded directly to the
driver via a new .read callback.

This avoids the need to read the entire region contents into memory first
and avoids the software overhead of creating a snapshot and then deleting
it.

This series implements such behavior and hooks up the ice NVM and shadow RAM
regions to allow it.

[1] https://lore.kernel.org/netdev/20200130225913.1671982-1-jacob.e.keller@intel.com/
====================

Link: https://lore.kernel.org/r/20221128203647.1198669-1-jacob.e.keller@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 18 insertions, 0 deletions

diff --git a/include/net/devlink.h b/include/net/devlink.h
index 074a79b8933f..02528f736f65 100644
--- a/include/net/devlink.h
+++ b/include/net/devlink.h
@@ -650,6 +650,10 @@ struct devlink_info_req;
  *            the data variable must be updated to point to the snapshot data.
  *            The function will be called while the devlink instance lock is
  *            held.
+ * @read: callback to directly read a portion of the region. On success,
+ *        the data pointer will be updated with the contents of the
+ *        requested portion of the region. The function will be called
+ *        while the devlink instance lock is held.
  * @priv: Pointer to driver private data for the region operation
  */
 struct devlink_region_ops {
@@ -659,6 +663,10 @@ struct devlink_region_ops {
 			const struct devlink_region_ops *ops,
 			struct netlink_ext_ack *extack,
 			u8 **data);
+	int (*read)(struct devlink *devlink,
+		    const struct devlink_region_ops *ops,
+		    struct netlink_ext_ack *extack,
+		    u64 offset, u32 size, u8 *data);
 	void *priv;
 };
 
@@ -670,6 +678,10 @@ struct devlink_region_ops {
  *            the data variable must be updated to point to the snapshot data.
  *            The function will be called while the devlink instance lock is
  *            held.
+ * @read: callback to directly read a portion of the region. On success,
+ *        the data pointer will be updated with the contents of the
+ *        requested portion of the region. The function will be called
+ *        while the devlink instance lock is held.
  * @priv: Pointer to driver private data for the region operation
  */
 struct devlink_port_region_ops {
@@ -679,6 +691,10 @@ struct devlink_port_region_ops {
 			const struct devlink_port_region_ops *ops,
 			struct netlink_ext_ack *extack,
 			u8 **data);
+	int (*read)(struct devlink_port *port,
+		    const struct devlink_port_region_ops *ops,
+		    struct netlink_ext_ack *extack,
+		    u64 offset, u32 size, u8 *data);
 	void *priv;
 };
 
diff --git a/include/uapi/linux/devlink.h b/include/uapi/linux/devlink.h
index 498d0d5d0957..70191d96af89 100644
--- a/include/uapi/linux/devlink.h
+++ b/include/uapi/linux/devlink.h
@@ -610,6 +610,8 @@ enum devlink_attr {
 	DEVLINK_ATTR_RATE_TX_PRIORITY,		/* u32 */
 	DEVLINK_ATTR_RATE_TX_WEIGHT,		/* u32 */
 
+	DEVLINK_ATTR_REGION_DIRECT,		/* flag */
+
 	/* add new attributes above here, update the policy in devlink.c */
 
 	__DEVLINK_ATTR_MAX,