linux-kernel - Re: [PATCH v1] i2c: imx: fix missing stop condition in single-master mode

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Message-ID: <Z2PlCXSG8qt5_3ni@eichest-laptop>
Date: Thu, 19 Dec 2024 10:19:05 +0100
From: Stefan Eichenberger <eichest@...il.com>
To: Andi Shyti <andi.shyti@...nel.org>
Cc: o.rempel@...gutronix.de, kernel@...gutronix.de, shawnguo@...nel.org,
	s.hauer@...gutronix.de, festevam@...il.com, Frank.Li@....com,
	stefan.eichenberger@...adex.com, francesco.dolcini@...adex.com,
	linux-i2c@...r.kernel.org, imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] i2c: imx: fix missing stop condition in single-master
 mode

Hi Andi,

On Wed, Dec 18, 2024 at 07:16:23PM +0100, Andi Shyti wrote:
> Hi Stefan,
> 
> On Mon, Dec 16, 2024 at 04:16:40PM +0100, Stefan Eichenberger wrote:
> > From: Stefan Eichenberger <stefan.eichenberger@...adex.com>
> > 
> > A regression was introduced with the implementation of single-master
> > mode, preventing proper stop conditions from being generated. Devices
> > that require a valid stop condition, such as EEPROMs, fail to function
> > correctly as a result.
> > 
> > The issue only affects devices with the single-master property enabled.
> > 
> > This commit resolves the issue by re-enabling I2C bus busy bit (IBB)
> > polling for single-master mode when generating a stop condition. The fix
> > further ensures that the i2c_imx->stopped flag is cleared at the start
> > of each transfer, allowing the stop condition to be correctly generated
> > in i2c_imx_stop().
> > 
> > According to the reference manual (IMX8MMRM, Rev. 2, 09/2019, page
> > 5270), polling the IBB bit to determine if the bus is free is only
> > necessary in multi-master mode. Consequently, the IBB bit is not polled
> > for the start condition in single-master mode.
> > 
> > Fixes: 6692694aca86 ("i2c: imx: do not poll for bus busy in single master mode")
> > Signed-off-by: Stefan Eichenberger <stefan.eichenberger@...adex.com>
> > ---
> >  drivers/i2c/busses/i2c-imx.c | 8 +++-----
> >  1 file changed, 3 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> > index f751d231ded8..cbf66a69e20b 100644
> > --- a/drivers/i2c/busses/i2c-imx.c
> > +++ b/drivers/i2c/busses/i2c-imx.c
> > @@ -534,20 +534,18 @@ static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx, int for_busy, bool a
> >  {
> >  	unsigned long orig_jiffies = jiffies;
> >  	unsigned int temp;
> > -
> > -	if (!i2c_imx->multi_master)
> > -		return 0;
> > +	bool multi_master = i2c_imx->multi_master;
> 
> with this small adjustment, I have applied your patch to 
> i2c/i2c-host-fixes.
> 
> The idea behind the change is that variables are sorted by 
> length, forming a kind of reversed Christmas tree shape. It's 
> not a strict rule—some communities enforce it, others don't, and 
> some follow entirely different conventions.
> 
> Since it feels somewhat arbitrary to me, I don't enforce it 
> strictly. However, I personally try to adhere to the reversed 
> Christmas tree rule whenever possible.

Thanks a lot for doing the change and for the explanation. I will keep
it in mind for future patches.

Best regards,
Stefan