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SubjectRE: [PATCH v4 1/3] mfd: Add new mfd device TPS68470
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Hi Andy,

> Subject: Re: [PATCH v4 1/3] mfd: Add new mfd device TPS68470
>
> On Fri, Jul 28, 2017 at 3:30 AM, Mani, Rajmohan
> <rajmohan.mani@intel.com> wrote:
> >> On Wed, Jul 26, 2017 at 11:23 AM, Lee Jones <lee.jones@linaro.org>
> wrote:
> >> > On Tue, 25 Jul 2017, Andy Shevchenko wrote:
> >> >> On Tue, Jul 25, 2017 at 12:10 PM, Lee Jones <lee.jones@linaro.org>
> wrote:
> >>
> >> >> I briefly checked few ->read() and ->write() implementations and
> >> >> didn't find any evidence of positive numbers that can be returned.
> >> >> Documentation (kernel doc) doesn't shed a light on that. So, to me
> >> >> it sounds unspecified.
> >> >>
> >> >> So, for now (until documentation will be fixed) I would rely on if
> >> >> (ret < 0)
> >> >
> >> > It's not unspecified. The regmap methods call into
> >> > regcache_write(), where the kerneldoc is clear.
> >>
> >
> > Since, we are interested in the regmap for the I2C bus here, I looked
> > into the implementation of
> > __devm_regmap_init()
> > __regmap_init()
> > regcache_init()
> > for I2C bus.
> >
> > At the end of __devm_regmap_init() call from devm_regmap_init_i2c()
> inside tps68470_probe(), I see that both cache_bypass and defer_caching
> flags of i2c regmap struct are set. So, it looks regcache_write/read calls do
> not come into play here.
> >
> > So, regmap_write()
> > _regmap_write()
> > map->reg_write (drivers/base/regmap/regmap.c:1665) translates
> to
> > regmap_i2c_write(drivers/base/regmap/regmap-i2c.c:128)
> >
> > These checks in regmap_i2c_write() ensure all return values from
> i2c_master_send() other than the requested number of bytes to write, are
> converted into negative values.
> >
> > if (ret == count)
> > return 0;
> > else if (ret < 0)
> > return ret;
> > else
> > return -EIO;
> >
> > Similar argument goes for regmap_read() as well.
> > With that, for regmap over I2C bus, it sounds like 'if (ret < 0)' looks to be a
> better choice. Please see if I missed anything here.
>
> It prooves exactly the Lee's point.
>
> So, perhaps the best approach is to move to if (ret) return ret;
>
> ...if it will be a problem in the future, fix it accordingly.
>

Ack.
We have spent enough time on this already.
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