On Wed, 13 Feb 2013 14:09:08 -0700, Stephen Warren wrote:
> On 02/13/2013 11:02 AM, Doug Anderson wrote:
> > The force_nr parameter to i2c_add_mux_adapter() uses 0 to signify that
> > we don't want to force the bus number of the adapter. This is
> > non-ideal because:
> > * 0 is actually a valid bus number to request
> > * i2c_add_numbered_adapter() (which i2c_add_mux_adapter() calls) uses
> > -1 to mean the same thing. That means extra logic in
> > i2c_add_mux_adapter().
> >
> > Fix i2c_add_mux_adapter() to use -1 and update all mux drivers
> > accordingly.
> >
> > Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx>
> > ---
> > Notes:
> > - If there's a good reason that force_nr uses 0 for auto then feel
> > free to drop this patch. I've place it at the end of the series to
> > make it easy to just drop it.
>
> IIRC (and I only vaguely do...) it's because:
>
> > diff --git a/drivers/i2c/muxes/i2c-mux-gpio.c b/drivers/i2c/muxes/i2c-mux-gpio.c
> > index 9f50ef0..301ed0b 100644
> > --- a/drivers/i2c/muxes/i2c-mux-gpio.c
> > +++ b/drivers/i2c/muxes/i2c-mux-gpio.c
> > @@ -208,7 +208,7 @@ static int i2c_mux_gpio_probe(struct platform_device *pdev)
> > }
> >
> > for (i = 0; i < mux->data.n_values; i++) {
> > - u32 nr = mux->data.base_nr ? (mux->data.base_nr + i) : 0;
> > + int nr = mux->data.base_nr ? (mux->data.base_nr + i) : -1;
>
> Here, mux->data.base_nr is platform data (or copied directly from it),
> and any field in a platform data struct stored in a global variable not
> explicitly initialized would be 0, hence 0 would typically mean "no
> explicit bus number desired". Since a mux can't exist without a parent
> I2C bus, it's unlikely anyone would want a mux to be I2C bus 0, but
> rather the parent to have that number.
Yes, as I recall this is exactly the reason why the current code is the
way it is.
--
Jean Delvare
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