linux-kernel - RE: [EXT] Re: [PATCH v2 1/3] i2c: imx-lpi2c: directly return ISR when detect a NACK

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Date:   Wed, 26 Jul 2023 07:58:27 +0000
From:   Carlos Song <carlos.song@....com>
To:     Andi Shyti <andi.shyti@...nel.org>
CC:     Aisheng Dong <aisheng.dong@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        Clark Wang <xiaoning.wang@....com>,
        Bough Chen <haibo.chen@....com>,
        dl-linux-imx <linux-imx@....com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [EXT] Re: [PATCH v2 1/3] i2c: imx-lpi2c: directly return ISR when
 detect a NACK

Hi, Andi

> -----Original Message-----
> From: Andi Shyti <andi.shyti@...nel.org>
> Sent: Wednesday, July 26, 2023 7:55 AM
> To: Carlos Song <carlos.song@....com>
> Cc: Aisheng Dong <aisheng.dong@....com>; shawnguo@...nel.org;
> s.hauer@...gutronix.de; kernel@...gutronix.de; festevam@...il.com; Clark
> Wang <xiaoning.wang@....com>; Bough Chen <haibo.chen@....com>;
> dl-linux-imx <linux-imx@....com>; linux-i2c@...r.kernel.org;
> linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org
> Subject: [EXT] Re: [PATCH v2 1/3] 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 Mon, Jul 24, 2023 at 06:55:44PM +0800, carlos.song@....com wrote:
> > From: Gao Pan <pandy.gao@....com>
> >
> > A NACK flag in ISR means i2c bus error. In such codition, there is no
> > need to do read/write operation. It's better to return ISR directly
> > and then stop i2c transfer.
> >
> > Fixes: a55fa9d0e42e ("i2c: imx-lpi2c: add low power i2c bus driver")
> > Signed-off-by: Gao Pan <pandy.gao@....com>
> > Signed-off-by: Carlos Song <carlos.song@....com>
> > ---
> >  drivers/i2c/busses/i2c-imx-lpi2c.c | 11 +++++------
> >  1 file changed, 5 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c
> > b/drivers/i2c/busses/i2c-imx-lpi2c.c
> > index c3287c887c6f..158de0b7f030 100644
> > --- a/drivers/i2c/busses/i2c-imx-lpi2c.c
> > +++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
> > @@ -514,15 +514,14 @@ static irqreturn_t lpi2c_imx_isr(int irq, void
> *dev_id)
> >       temp = readl(lpi2c_imx->base + LPI2C_MSR);
> >       temp &= enabled;
> >
> > -     if (temp & MSR_RDF)
> > +     if (temp & MSR_NDF) {
> > +             complete(&lpi2c_imx->complete);
> > +             return IRQ_HANDLED;
> 
> you can actually remove the return here
> 
>         if (temp & MSR_NDF)
>                 complete();
>         else if (temp & MSR_RDF)
>                 exfifo();
>         else if (temp & MSR_TDF)
>                 txfifo();
> 
>         return IRQ_HANDLED;
> 
> 
> BTW, the logic here is changing, as well and it's not described in the commit log.
> This patch is not only stopping when a nack is received (MSR_NDF), but it's also
> making mutually exclusive read/write (which I guess are MSR_RDF and
> MSR_TDF).
> 
> Is this what you want? If so, can you please describe it in the commit log or add
> a comment describing that the three states are all mutually exclusive.
> 
Yes. That is ok. I will fix the commit log and send V3 patch.
> Thanks,
> Andi
> 
> 
> > +     } else if (temp & MSR_RDF)
> >               lpi2c_imx_read_rxfifo(lpi2c_imx);
> > -
> > -     if (temp & MSR_TDF)
> > +     else if (temp & MSR_TDF)
> >               lpi2c_imx_write_txfifo(lpi2c_imx);
> >
> > -     if (temp & MSR_NDF)
> > -             complete(&lpi2c_imx->complete);
> > -
> >       return IRQ_HANDLED;
> >  }
> >
> > --
> > 2.34.1
> >