[PATCH 3/3] mailbox: mpfs: account for mbox offsets while sending

[Conor Dooley <conor.dooley@microchip.com>]

The mailbox offset is not only used for receiving messages, but it is
also used by messages sent to the system controller by Linux that have a
payload, such as the "digital signature service". It is also overloaded
by certain other services (reprogramming of the FPGA fabric, see Link:)
to have a meaning other than the offset the system controller should
read from.
When the driver was written, no such services of the latter type were
in use & those of the former used an offset of zero so this has gone
un-noticed.

Link: https://www.microsemi.com/document-portal/doc_download/1245815-polarfire-fpga-and-polarfire-soc-fpga-system-services-user-guide # Section 5.2
Fixes: 83d7b1560810 ("mbox: add polarfire soc system controller mailbox")
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
 drivers/mailbox/mailbox-mpfs.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/mailbox/mailbox-mpfs.c b/drivers/mailbox/mailbox-mpfs.c
index e432a8f0d148..cfacb3f320a6 100644
--- a/drivers/mailbox/mailbox-mpfs.c
+++ b/drivers/mailbox/mailbox-mpfs.c
@@ -100,21 +100,20 @@ static int mpfs_mbox_send_data(struct mbox_chan *chan, void *data)
 
 		for (index = 0; index < (msg->cmd_data_size / 4); index++)
 			writel_relaxed(word_buf[index],
-				       mbox->mbox_base + index * 0x4);
+				       mbox->mbox_base + msg->mbox_offset + index * 0x4);
 		if (extra_bits) {
 			u8 i;
 			u8 byte_off = ALIGN_DOWN(msg->cmd_data_size, 4);
 			u8 *byte_buf = msg->cmd_data + byte_off;
 
-			val = readl_relaxed(mbox->mbox_base + index * 0x4);
+			val = readl_relaxed(mbox->mbox_base + msg->mbox_offset + index * 0x4);
 
 			for (i = 0u; i < extra_bits; i++) {
 				val &= ~(0xffu << (i * 8u));
 				val |= (byte_buf[i] << (i * 8u));
 			}
 
-			writel_relaxed(val,
-				       mbox->mbox_base + index * 0x4);
+			writel_relaxed(val, mbox->mbox_base + msg->mbox_offset + index * 0x4);
 		}
 	}
 
-- 
2.36.1