[PATCH 10/22] firmware: ti_sci: Use tx_message as message buffer directly

[Beleswar Padhi]

From: Andrew Davis <afd@xxxxxx>

As we now have the tx_message during the whole xfer process we can use
that as our message buffer to be sent. This removes an extra copy.

Note: the mailbox framework keeps only a pointer to tx_message and may
submit it after ti_sci_do_xfer() returns if it was queued behind
other messages. But, this cannot happen in practice: messages expecting
a response are always submitted before their callers return, and the
only no-response message (PREPARE_SLEEP for Partial-IO) is sent from the
power-off handler with other CPUs stopped, after which nothing else uses
the TX channel.

Signed-off-by: Andrew Davis <afd@xxxxxx>
Co-developed-by: Beleswar Padhi <b-padhi@xxxxxx>
Signed-off-by: Beleswar Padhi <b-padhi@xxxxxx>
---
Note:
To avoid KASAN warnings, and possible duplicate message resend, it's
better for the following ti-msgmgr mbox patch series to be applied
before this one goes in:
https://lore.kernel.org/all/20260929200159.4033010-1-b-padhi@xxxxxx/

 drivers/firmware/ti_sci.c | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/drivers/firmware/ti_sci.c b/drivers/firmware/ti_sci.c
index dbe192142bf17..6ed67160c6a7f 100644
--- a/drivers/firmware/ti_sci.c
+++ b/drivers/firmware/ti_sci.c
@@ -43,18 +43,13 @@ static DEFINE_MUTEX(ti_sci_list_mutex);
 /**
  * struct ti_sci_xfer - Structure representing a message flow
  * @tx_message:	Transmit message
- * @tx_buf:	Pointer to the message to send
  * @rx_buf:	Pointer to store received message
  * @rx_len:	Receive message length
  * @xfer_buf:	Preallocated buffer to store receive message
- *		Since we work with request-ACK protocol, we can
- *		reuse the same buffer for the rx path as we
- *		use for the tx path.
  * @done:	completion event
  */
 struct ti_sci_xfer {
 	struct ti_msgmgr_message tx_message;
-	void *tx_buf;
 	void *rx_buf;
 	u8 rx_len;
 	u8 *xfer_buf;
@@ -372,16 +367,16 @@ static struct ti_sci_xfer *ti_sci_get_one_xfer(struct ti_sci_info *info,
 
 	xfer = &minfo->xfer_block[xfer_id];
 
-	hdr = (struct ti_sci_msg_hdr *)xfer->tx_message.buf;
 	xfer->tx_message.len = tx_message_size;
 	xfer->tx_message.chan_rx = info->chan_rx;
 	xfer->tx_message.timeout_rx_ms = info->desc->max_rx_timeout_ms;
-	xfer->tx_buf = tx_message;
+	xfer->tx_message.buf = tx_message;
 	xfer->rx_buf = rx_message;
 	xfer->rx_len = (u8)rx_message_size;
 
 	reinit_completion(&xfer->done);
 
+	hdr = (struct ti_sci_msg_hdr *)tx_message;
 	hdr->seq = xfer_id;
 	hdr->type = msg_type;
 	hdr->host = info->host_id;
@@ -487,10 +482,6 @@ static inline int ti_sci_do_xfer(const struct ti_sci_handle *handle,
 	if (IS_ERR(xfer))
 		return PTR_ERR(xfer);
 
-	memcpy(xfer->xfer_buf + sizeof(struct ti_sci_msg_hdr),
-	       xfer->tx_buf + sizeof(struct ti_sci_msg_hdr),
-	       xfer->tx_message.len - sizeof(struct ti_sci_msg_hdr));
-
 	ret = mbox_send_message(info->chan_tx, &xfer->tx_message);
 	if (ret < 0) {
 		dev_err(dev, "Mbox send fail %d (caller: %pS)\n", ret, caller);
@@ -3396,7 +3387,6 @@ static int ti_sci_probe(struct platform_device *pdev)
 		if (!xfer->xfer_buf)
 			return -ENOMEM;
 
-		xfer->tx_message.buf = xfer->xfer_buf;
 		init_completion(&xfer->done);
 	}
 
-- 
2.34.1