linux-kernel - Re: [PATCH v2 2/7] i2c: npcm: correct the read/write operation procedure

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Message-ID: <CAHb3i=sHzF8p572SBMvfCVQmo+7VcYbOYuqUU-H2sEiTkfWD7A@mail.gmail.com>
Date: Sun, 8 Sep 2024 13:39:08 +0300
From: Tali Perry <tali.perry1@...il.com>
To: Andi Shyti <andi.shyti@...nel.org>
Cc: Tyrone Ting <warp5tw@...il.com>, avifishman70@...il.com, tmaimon77@...il.com, 
	venture@...gle.com, yuenn@...gle.com, benjaminfair@...gle.com, 
	andriy.shevchenko@...ux.intel.com, wsa@...nel.org, rand.sec96@...il.com, 
	wsa+renesas@...g-engineering.com, tali.perry@...oton.com, 
	Avi.Fishman@...oton.com, tomer.maimon@...oton.com, KWLIU@...oton.com, 
	JJLIU0@...oton.com, kfting@...oton.com, openbmc@...ts.ozlabs.org, 
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/7] i2c: npcm: correct the read/write operation procedure

Hi Andi,

On Fri, Sep 6, 2024 at 12:29 AM Andi Shyti <andi.shyti@...nel.org> wrote:
>
> Hi Tyronne,
>
> On Fri, Aug 30, 2024 at 11:46:35AM GMT, Tyrone Ting wrote:
> > Originally the driver uses the XMIT bit in SMBnST register to decide
> > the upcoming i2c transaction. If XMIT bit is 1, then it will be an i2c
> > write operation. If it's 0, then a read operation will be executed.
> >
> > After checking the datasheet, the XMIT bit is valid when the i2c module
> > is acting in a slave role. Use the software status to control the i2c
> > transaction flow instead when the i2c module is acting in a master role.
> >
> > Fixes: 48acf8292280 ("i2c: Remove redundant comparison in npcm_i2c_reg_slave")
>
> Fixes needs to be used if you are fixing a bug (crash,
> device malfunction, etc.). If you want to use it, please describe
> the bug you are fixing. Otherwise, please, remove it.
>
> > Signed-off-by: Tyrone Ting <kfting@...oton.com>
> > ---
> >  drivers/i2c/busses/i2c-npcm7xx.c | 7 ++-----
> >  1 file changed, 2 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-npcm7xx.c b/drivers/i2c/busses/i2c-npcm7xx.c
> > index bbcb4d6668ce..2b76dbfba438 100644
> > --- a/drivers/i2c/busses/i2c-npcm7xx.c
> > +++ b/drivers/i2c/busses/i2c-npcm7xx.c
> > @@ -1628,13 +1628,10 @@ static void npcm_i2c_irq_handle_sda(struct npcm_i2c *bus, u8 i2cst)
> >                       npcm_i2c_wr_byte(bus, bus->dest_addr | BIT(0));
> >       /* SDA interrupt, after start\restart */
> >       } else {
> > -             if (NPCM_I2CST_XMIT & i2cst) {
> > -                     bus->operation = I2C_WRITE_OPER;
> > +             if (bus->operation == I2C_WRITE_OPER)
> >                       npcm_i2c_irq_master_handler_write(bus);
> > -             } else {
> > -                     bus->operation = I2C_READ_OPER;
> > +             else if (bus->operation == I2C_READ_OPER)
> >                       npcm_i2c_irq_master_handler_read(bus);
>
> mmmhhh... you are changing the logic here and you are not
> describing the logic change in the commit log.
>
> Without looking at the details, if this is a state machine you
> are breaking it.
>
> Can anyone from the ARM/NUVOTON NPCM supporters and reviewers
> take a look at this patch?
>

Indeed, the driver can use both the register bits or the state machine
to determine the current state of the bus.
In slave mode the XMIT bit can simply be used directly to set the state.
XMIT bit can be used as indication to the current state of the state
machine during slave operation.
(meaning XMIT = 1 during writing and XMIT = 0 during reading).
In master operation XMIT is valid only if there are no bus errors.
For example: in a multi master where the same module is switching from
master to slave at runtime, and there are collisions,
the XMIT bit cannot be trusted.
However the maser already "knows" what the bus state is, so this bit
is not needed and the driver can just track
what it is currently doing.




> Thanks,
> Andi
>
> > -             }
> >       }
> >  }
> >
> > --
> > 2.34.1
> >