Re: [PATCH] i2c: mediatek: fix potential incorrect use of I2C_MASTER_WRRD

["Leilk Liu (刘磊)" <Leilk.Liu@mediatek.com>]

On Tue, 2025-08-19 at 20:09 -0100, Andi Shyti wrote:
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> 
Hi Andi, sorry for late reply.

> Hi Leilk,
> 
> On Sat, Aug 16, 2025 at 03:53:54PM +0800, Leilk Liu wrote:
> > From: "Leilk.Liu" <leilk.liu@mediatek.com>
> > 
> > The old IC does not support the I2C_MASTER_WRRD (write-then-read)
> > function, but the current code’s handling of i2c->auto_restart may
> > potentially lead to entering the I2C_MASTER_WRRD software flow,
> > resulting in unexpected bugs.
> 
> do you mean unexpected behaviour?
sure.

> 
> > Instead of repurposing the auto_restart flag, add a separate flag
> > to signal I2C_MASTER_WRRD operations.
> > 
> > Also fix handling of msgs. If the operation (i2c->op) is
> > I2C_MASTER_WRRD, then the msgs pointer is incremented by 2.
> > For all other operations, msgs is simply incremented by 1.
> > 
> > Fixes: 173b77e8d8fe ("i2c: mediatek: add i2c first write then read
> > optimization")
> > 
> 
> No need for blank line here. BTW, this doesn't look the commit
> that is introducing the issue.
> 
OK.
Fixes:b2ed11e224a2 ("I2C: mediatek: Add driver for MediaTek MT8173 I2C
controller")

> > Signed-off-by: Leilk.Liu <leilk.liu@mediatek.com>
> > ---
> >  drivers/i2c/busses/i2c-mt65xx.c | 17 ++++++++++-------
> >  1 file changed, 10 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-mt65xx.c
> > b/drivers/i2c/busses/i2c-mt65xx.c
> > index ab456c3717db..dee40704825c 100644
> > --- a/drivers/i2c/busses/i2c-mt65xx.c
> > +++ b/drivers/i2c/busses/i2c-mt65xx.c
> > @@ -1243,6 +1243,7 @@ static int mtk_i2c_transfer(struct
> > i2c_adapter *adap,
> >  {
> >       int ret;
> >       int left_num = num;
> > +     bool write_then_read_en = false;
> >       struct mtk_i2c *i2c = i2c_get_adapdata(adap);
> > 
> >       ret = clk_bulk_enable(I2C_MT65XX_CLK_MAX, i2c->clocks);
> > @@ -1256,6 +1257,7 @@ static int mtk_i2c_transfer(struct
> > i2c_adapter *adap,
> >               if (!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags &
> > I2C_M_RD) &&
> >                   msgs[0].addr == msgs[1].addr) {
> >                       i2c->auto_restart = 0;
> > +                     write_then_read_en = true;
> 
> why don't we set "i2c->op = I2C_MASTER_WRRD" here and avoid an
> extra flag?
> 
we need to set "i2c->op" again in the following code, so an extra flag
is necessary.

> Thanks,
> Andi
> 
> >               }
> >       }
> >