[PATCH v1] arch: arm: mach-socfpga: Mailbox buffer and SDM doorbell improvement

[Chee, Tien Fong]

-----Original Message-----
From: Yuslaimi, Alif Zakuan <alif.zakuan.yuslaimi at intel.com> 
Sent: Wednesday, January 22, 2025 10:21 AM
To: u-boot at lists.denx.de
Cc: Marek Vasut <marex at denx.de>; Simon Goldschmidt <simon.k.r.goldschmidt at gmail.com>; Chee, Tien Fong <tien.fong.chee at intel.com>; Tom Rini <trini at konsulko.com>; Alif Zakuan Yuslaimi <alif.zakuan.yuslaimi at altera.com>; Simon Glass <sjg at chromium.org>
Subject: [PATCH v1] arch: arm: mach-socfpga: Mailbox buffer and SDM doorbell improvement

From: Alif Zakuan Yuslaimi <alif.zakuan.yuslaimi at altera.com>

The current write and notify SDM to read mechanism has a flaw where SDM is not notified enough to be able to read all the data in the buffer.

This is caused by SDM doorbell will only be sent out once the command buffer overflow check is satisfied. If the command buffer does not reach overflow status, no SDM doorbell will be sent out, which may cause a timeout as the mailbox driver will be waiting for the SDM to read the buffer to empty even though SDM is not notified to do so.

The solution is to remove the command buffer overflow check and set the SDM doorbell to always trigger at the end of the command buffer.

This will ensure that the SDM is able to read all of the data.

Signed-off-by: Alif Zakuan Yuslaimi <alif.zakuan.yuslaimi at altera.com>
---
 arch/arm/mach-socfpga/mailbox_s10.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/arch/arm/mach-socfpga/mailbox_s10.c b/arch/arm/mach-socfpga/mailbox_s10.c
index 2b4f26040fe..b69bd3e47ec 100644
--- a/arch/arm/mach-socfpga/mailbox_s10.c
+++ b/arch/arm/mach-socfpga/mailbox_s10.c
@@ -88,6 +88,8 @@ static __always_inline int mbox_write_cmd_buffer(u32 *cin, u32 data,
 			MBOX_WRITE_CMD_BUF(data, (*cin)++);
 			*cin %= MBOX_CMD_BUFFER_SIZE;
 			MBOX_WRITEL(*cin, MBOX_CIN);
+			if (is_cmdbuf_overflow)
+				*is_cmdbuf_overflow = 0;
 			break;
 		}
 		timeout--;
@@ -96,10 +98,6 @@ static __always_inline int mbox_write_cmd_buffer(u32 *cin, u32 data,
 	if (!timeout)
 		return -ETIMEDOUT;
 
-	/* Wait for the SDM to drain the FIFO command buffer */
-	if (is_cmdbuf_overflow && *is_cmdbuf_overflow)
-		return mbox_wait_for_cmdbuf_empty(*cin);
-
 	return 0;
 }
 
@@ -125,13 +123,11 @@ static __always_inline int mbox_fill_cmd_circular_buff(u32 header, u32 len,
 			return ret;
 	}
 
-	/* If SDM doorbell is not triggered after the last data is
-	 * written into mailbox FIFO command buffer, trigger the
-	 * SDM doorbell again to ensure SDM able to read the remaining
-	 * data.
+	/*
+	 * Always trigger the SDM doorbell at the end to ensure SDM able to read
+	 * the remaining data.
 	 */
-	if (!is_cmdbuf_overflow)
-		MBOX_WRITEL(1, MBOX_DOORBELL_TO_SDM);
+	MBOX_WRITEL(1, MBOX_DOORBELL_TO_SDM);
 
 	return 0;
 }
--
2.25.1

Reviewed-by: Tien Fong Chee <tien.fong.chee at intel.com>

Best regards,
Tien Fong