[PATCH v3] i2c: imx-lpi2c: directly return ISR when detect a NACK

[PATCH v3] i2c: imx-lpi2c: directly return ISR when detect a NACK

[carlos.song]

From: Carlos Song <carlos.song@nxp.com>

A NACK flag in ISR means i2c bus error. In such condition,
there is no need to do read/write operation.

In this patch, i2c will check MSR_NDF, MSR_RDF and MSR_TDF
flag in turn, it's making mutually exclusive NACK/read/write.
So when a NACK is received(MSR_NDF), i2c will return ISR
directly and then stop i2c transfer.

Fixes: a55fa9d0e42e ("i2c: imx-lpi2c: add low power i2c bus driver")
Signed-off-by: Carlos Song <carlos.song@nxp.com>
---
Changes for V3:
- modify commit log
- modify Signed-off-by list
---
 drivers/i2c/busses/i2c-imx-lpi2c.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c b/drivers/i2c/busses/i2c-imx-lpi2c.c
index c3287c887c6f..636ad3247982 100644
--- a/drivers/i2c/busses/i2c-imx-lpi2c.c
+++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
@@ -514,14 +514,12 @@ static irqreturn_t lpi2c_imx_isr(int irq, void *dev_id)
 	temp = readl(lpi2c_imx->base + LPI2C_MSR);
 	temp &= enabled;
 
-	if (temp & MSR_RDF)
-		lpi2c_imx_read_rxfifo(lpi2c_imx);
-
-	if (temp & MSR_TDF)
-		lpi2c_imx_write_txfifo(lpi2c_imx);
-
 	if (temp & MSR_NDF)
 		complete(&lpi2c_imx->complete);
+	else if (temp & MSR_RDF)
+		lpi2c_imx_read_rxfifo(lpi2c_imx);
+	else if (temp & MSR_TDF)
+		lpi2c_imx_write_txfifo(lpi2c_imx);
 
 	return IRQ_HANDLED;
 }
-- 
2.34.1

Re: [PATCH v3] i2c: imx-lpi2c: directly return ISR when detect a NACK

[Andi Shyti]

Hi Carlos,

On Wed, Jul 26, 2023 at 05:23:50PM +0800, carlos.song@nxp.com wrote:
> From: Carlos Song <carlos.song@nxp.com>
> 
> A NACK flag in ISR means i2c bus error. In such condition,
> there is no need to do read/write operation.
> 
> In this patch, i2c will check MSR_NDF, MSR_RDF and MSR_TDF
> flag in turn, it's making mutually exclusive NACK/read/write.
> So when a NACK is received(MSR_NDF), i2c will return ISR
> directly and then stop i2c transfer.

Very good, thank you!

> Fixes: a55fa9d0e42e ("i2c: imx-lpi2c: add low power i2c bus driver")

One last little question here. I want to know if this is actually
fixing something or cleaning the exit path. What I mean is:
can the device ever send an NDF along with an RDF or TDF?

If not, this "Fixes:" tag should be removed and this patch can be
considered a cleanup. Otherwise would be nice to know what
failure are you fixing.

I'm just trying to understand here :)

Andi

RE: [EXT] Re: [PATCH v3] i2c: imx-lpi2c: directly return ISR when detect a NACK

[Carlos Song]

> -----Original Message-----
> From: Andi Shyti <andi.shyti@kernel.org>
> Sent: Wednesday, July 26, 2023 10:52 PM
> To: Carlos Song <carlos.song@nxp.com>
> Cc: Aisheng Dong <aisheng.dong@nxp.com>; shawnguo@kernel.org;
> s.hauer@pengutronix.de; kernel@pengutronix.de; festevam@gmail.com; Clark
> Wang <xiaoning.wang@nxp.com>; Bough Chen <haibo.chen@nxp.com>;
> dl-linux-imx <linux-imx@nxp.com>; linux-i2c@vger.kernel.org;
> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org
> Subject: [EXT] Re: [PATCH v3] i2c: imx-lpi2c: directly return ISR when detect a
> NACK
> 
> Caution: This is an external email. Please take care when clicking links or
> opening attachments. When in doubt, report the message using the 'Report this
> email' button
> 
> 
> Hi Carlos,
> 
> On Wed, Jul 26, 2023 at 05:23:50PM +0800, carlos.song@nxp.com wrote:
> > From: Carlos Song <carlos.song@nxp.com>
> >
> > A NACK flag in ISR means i2c bus error. In such condition, there is no
> > need to do read/write operation.
> >
> > In this patch, i2c will check MSR_NDF, MSR_RDF and MSR_TDF flag in
> > turn, it's making mutually exclusive NACK/read/write.
> > So when a NACK is received(MSR_NDF), i2c will return ISR directly and
> > then stop i2c transfer.
> 
> Very good, thank you!
> 
> > Fixes: a55fa9d0e42e ("i2c: imx-lpi2c: add low power i2c bus driver")
> 
> One last little question here. I want to know if this is actually fixing something or
> cleaning the exit path. What I mean is:
> can the device ever send an NDF along with an RDF or TDF?
> 
> If not, this "Fixes:" tag should be removed and this patch can be considered a
> cleanup. Otherwise would be nice to know what failure are you fixing.
> 
> I'm just trying to understand here :)
>
> Andi


Hi, Andi,
Yes, no failure to fix just a cleanup. I will remove it and resend v4.