linux-kernel - [PATCH] i2c: cadence: Avoid fifo clear after start

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Date: Fri, 5 Jan 2024 18:22:58 +0530
From: Sai Pavan Boddu <sai.pavan.boddu@....com>
To: <linux-kernel@...r.kernel.org>, <linux-i2c@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
CC: Michal Simek <michal.simek@....com>, Andi Shyti <andi.shyti@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>, Wolfram Sang <wsa@...nel.org>
Subject: [PATCH] i2c: cadence: Avoid fifo clear after start

Driver unintentionally programs ctrl reg to clear fifo which is
happening after start of transaction, this was not the case previously
as it was read-modified-write. This issue breaks i2c reads on QEMU as
i2c-read is done before guest starts programming ctrl register.

Fixes: ff0cf7bca6309 ("i2c: cadence: Remove unnecessary register reads")
Signed-off-by: Sai Pavan Boddu <sai.pavan.boddu@....com>
---
 drivers/i2c/busses/i2c-cadence.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
index de3f58b60dce..6f7d753a8197 100644
--- a/drivers/i2c/busses/i2c-cadence.c
+++ b/drivers/i2c/busses/i2c-cadence.c
@@ -633,6 +633,7 @@ static void cdns_i2c_mrecv(struct cdns_i2c *id)
 
 	if (hold_clear) {
 		ctrl_reg &= ~CDNS_I2C_CR_HOLD;
+		ctrl_reg &= ~CDNS_I2C_CR_CLR_FIFO;
 		/*
 		 * In case of Xilinx Zynq SOC, clear the HOLD bit before transfer size
 		 * register reaches '0'. This is an IP bug which causes transfer size
-- 
2.25.1