[PATCH v5 2/3] I2C: mediatek: Add driver for MediaTek I2C controller
Eddie Huang
eddie.huang at mediatek.com
Tue Mar 31 00:08:35 PDT 2015
Hi Sascha,
On Mon, 2015-03-30 at 19:23 +0200, Sascha Hauer wrote:
> On Mon, Mar 30, 2015 at 04:14:12PM +0800, Eddie Huang wrote:
> > Hi Sascha,
> >
> > >
> > > [...]
> > >
> > > > + if (i2c->speed_hz > 400000)
> > > > + control_reg |= I2C_CONTROL_RS;
> > > > + if (i2c->op == I2C_MASTER_WRRD)
> > > > + control_reg |= I2C_CONTROL_DIR_CHANGE | I2C_CONTROL_RS;
> > > > + mtk_i2c_writew(control_reg, i2c, OFFSET_CONTROL);
> > > > +
> > > > + /* set start condition */
> > > > + if (i2c->speed_hz <= 100000)
> > > > + mtk_i2c_writew(I2C_ST_START_CON, i2c, OFFSET_EXT_CONF);
> > > > + else
> > > > + mtk_i2c_writew(I2C_FS_START_CON, i2c, OFFSET_EXT_CONF);
> > > > +
> > > > + if (~control_reg & I2C_CONTROL_RS)
> > > > + mtk_i2c_writew(I2C_DELAY_LEN, i2c, OFFSET_DELAY_LEN);
> > >
> > > speed <= 400000 here to make this more obvious?
> > There are two cases, not only speed<=400000, but I2C_MASTER_WRRD. I tend
> > to keep it.
>
> Still it looks strange. You only ever write this default value to the
> register. Putting this register write under an if() seems bogus since
> the same value will be in the register the next time this code is
> executed. It looks like you should move this register write to some
> initialization function.
OK, move to mtk_i2c_init_hw function
>
> > > > +
> > > > + /* Enable interrupt */
> > > > + mtk_i2c_writew(I2C_HS_NACKERR | I2C_ACKERR | I2C_TRANSAC_COMP,
> > > > + i2c, OFFSET_INTR_MASK);
> > >
> > > Why do you enable/disable interrupts for each transfer? Enabling them
> > > once and just acknowledge them in the interrupt handler should be
> > > enough.
> > This can avoid unwanted I2C interrupt. For example, I2C transfer error,
> > and cause timeout, I2C driver report error to caller. Then I2C error
> > interrupt happen.
>
> So isn't the same unwanted interrupt then just delayed until you enable
> the interrupts again? Is this something that really happens or just
> something you think that might happen?
>
Clear interrupt status before enable interrupt, so won't get unwanted
interrupt again. I just think this might happen, and it's not harmful to
enable/disable interrupt in transfer function and can get extra benefit
to avoid unnecessary interrupt. Tegra I2C driver i2c-tegra.c also do
the same thing.
Eddie
More information about the Linux-mediatek
mailing list