linux-kernel - [PATCH] i2c: mpc: Use atomic read and fix break condition

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Date:   Tue,  7 Dec 2021 17:21:44 +1300
From:   Chris Packham <chris.packham@...iedtelesis.co.nz>
To:     wsa@...nel.org, mbizon@...ebox.fr
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chris Packham <chris.packham@...iedtelesis.co.nz>
Subject: [PATCH] i2c: mpc: Use atomic read and fix break condition

Maxime points out that the polling code in mpc_i2c_isr should use the
_atomic API because it is called in an irq context and that the
behaviour of the MCF bit is that it is 1 when the byte transfer is
complete. All of this means the original code was effectively a
udelay(100).

Fix this by using readb_poll_timeout_atomic() and removing the negation
of the break condition.

Fixes: 4a8ac5e45cda ("i2c: mpc: Poll for MCF")
Reported-by: Maxime Bizon <mbizon@...ebox.fr>
Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
---

Maxime,

Can you give this a test on your setup. I've tried it on the setup where
I had the original problem that led to 4a8ac5e45cda and it seems OK so
far (I'll leave my test running overnight).

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

diff --git a/drivers/i2c/busses/i2c-mpc.c b/drivers/i2c/busses/i2c-mpc.c
index a6ea1eb1394e..53b8da6dbb23 100644
--- a/drivers/i2c/busses/i2c-mpc.c
+++ b/drivers/i2c/busses/i2c-mpc.c
@@ -636,7 +636,7 @@ static irqreturn_t mpc_i2c_isr(int irq, void *dev_id)
 	status = readb(i2c->base + MPC_I2C_SR);
 	if (status & CSR_MIF) {
 		/* Wait up to 100us for transfer to properly complete */
-		readb_poll_timeout(i2c->base + MPC_I2C_SR, status, !(status & CSR_MCF), 0, 100);
+		readb_poll_timeout_atomic(i2c->base + MPC_I2C_SR, status, status & CSR_MCF, 0, 100);
 		writeb(0, i2c->base + MPC_I2C_SR);
 		mpc_i2c_do_intr(i2c, status);
 		return IRQ_HANDLED;
-- 
2.34.1