linux-kernel - [PATCH] i2c: microchip-core: fix erroneous late ack send

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Date:   Fri, 5 Aug 2022 08:43:46 +0100
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     Wolfram Sang <wsa@...nel.org>,
        Daire McNamara <daire.mcnamara@...rochip.com>
CC:     Conor Dooley <conor.dooley@...rochip.com>,
        <linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Andreas Buerkler <andreas.buerkler@...lustra.com>,
        Lewis Hanly <lewis.hanly@...rochip.com>
Subject: [PATCH] i2c: microchip-core: fix erroneous late ack send

A late ack is currently being sent at the end of a transfer due to
incorrect logic in mchp_corei2c_empty_rx(). Currently the Assert Ack
bit is being written to the controller's control reg after the last
byte has been received, causing it to sent another byte with the ack.
Instead, the AA flag should be written to to the contol register when
the penultimate byte is read so it is sent out for the last byte.

Reported-by: Andreas Buerkler <andreas.buerkler@...lustra.com>
Fixes: 64a6f1c4987e ("i2c: add support for microchip fpga i2c controllers")
Tested-by: Lewis Hanly <lewis.hanly@...rochip.com>
Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
---

FYI Wolfram, I am still sitting on the MAINTAINERS update as the
SoC updates have not been pulled yet for 6.0 (AFAICT)

 drivers/i2c/busses/i2c-microchip-corei2c.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-microchip-corei2c.c b/drivers/i2c/busses/i2c-microchip-corei2c.c
index 6df0f1c33278..4d7e9b25f018 100644
--- a/drivers/i2c/busses/i2c-microchip-corei2c.c
+++ b/drivers/i2c/busses/i2c-microchip-corei2c.c
@@ -206,7 +206,7 @@ static void mchp_corei2c_empty_rx(struct mchp_corei2c_dev *idev)
 		idev->msg_len--;
 	}
 
-	if (idev->msg_len == 0) {
+	if (idev->msg_len <= 1) {
 		ctrl = readb(idev->base + CORE_I2C_CTRL);
 		ctrl &= ~CTRL_AA;
 		writeb(ctrl, idev->base + CORE_I2C_CTRL);
-- 
2.36.1