[RFC PATCH 5/7] firmware: arm_scmi: Add xfer_init_buffers transport op

[Peter Hilber <peter.hilber@opensynergy.com>]

From: Igor Skalkin <igor.skalkin@opensynergy.com>

The virtio transport in this patch series can be simplified by using the
scmi_xfer tx/rx buffers for data exchange with the virtio device, and
for saving the message state. But the virtio transport requires
prepending a transport-specific header. Also, for data exchange using
virtqueues, the tx and rx buffers should not overlap.

After the previous patch, this is the second and final step to enable
the virtio transport to use the scmi_xfer buffers for data exchange.

Add an optional op through which the transport can allocate the tx/rx
buffers along with room for the prepended transport-specific headers.

Co-developed-by: Peter Hilber <peter.hilber@opensynergy.com>
Signed-off-by: Peter Hilber <peter.hilber@opensynergy.com>
Signed-off-by: Igor Skalkin <igor.skalkin@opensynergy.com>
---
 drivers/firmware/arm_scmi/common.h |  3 +++
 drivers/firmware/arm_scmi/driver.c | 21 +++++++++++++++------
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
index e3ccec954e93..c6071ffe4346 100644
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -206,6 +206,7 @@ struct scmi_chan_info {
  * @get_max_msg: Optional callback to provide max_msg dynamically
  * 	@max_msg: Maximum number of messages for the channel type (tx or rx)
  * 		that can be pending simultaneously in the system
+ * @xfer_init_buffers: Callback to initialize buffers for scmi_xfer
  * @send_message: Callback to send a message
  * @mark_txdone: Callback to mark tx as done
  * @fetch_response: Callback to fetch response
@@ -220,6 +221,8 @@ struct scmi_transport_ops {
 	int (*chan_free)(int id, void *p, void *data);
 	int (*get_max_msg)(bool tx, struct scmi_chan_info *base_cinfo,
 			   int *max_msg);
+	int (*xfer_init_buffers)(struct scmi_chan_info *cinfo,
+				 struct scmi_xfer *xfer, int max_msg_size);
 	int (*send_message)(struct scmi_chan_info *cinfo,
 			    struct scmi_xfer *xfer);
 	void (*mark_txdone)(struct scmi_chan_info *cinfo, int ret);
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index d66f19b27c44..2e25f6f068f5 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -632,12 +632,21 @@ static int __scmi_xfer_info_init(struct scmi_info *sinfo,
 
 	/* Pre-initialize the buffer pointer to pre-allocated buffers */
 	for (i = 0, xfer = info->xfer_block; i < info->max_msg; i++, xfer++) {
-		xfer->rx.buf = devm_kcalloc(dev, sizeof(u8), desc->max_msg_size,
-					    GFP_KERNEL);
-		if (!xfer->rx.buf)
-			return -ENOMEM;
-
-		xfer->tx.buf = xfer->rx.buf;
+		if (desc->ops->xfer_init_buffers) {
+			int ret = desc->ops->xfer_init_buffers(
+				base_cinfo, xfer, desc->max_msg_size);
+
+			if (ret)
+				return ret;
+		} else {
+			xfer->rx.buf = devm_kcalloc(dev, sizeof(u8),
+						    desc->max_msg_size,
+						    GFP_KERNEL);
+			if (!xfer->rx.buf)
+				return -ENOMEM;
+
+			xfer->tx.buf = xfer->rx.buf;
+		}
 		init_completion(&xfer->done);
 	}
 
-- 
2.25.1