[lkml]   [2017]   [Jul]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRE: [PATCH v4 1/3] mfd: Add new mfd device TPS68470
Hi Lee, Andy,

> Subject: Re: [PATCH v4 1/3] mfd: Add new mfd device TPS68470
> On Wed, Jul 26, 2017 at 11:23 AM, Lee Jones <> wrote:
> > On Tue, 25 Jul 2017, Andy Shevchenko wrote:
> >> On Tue, Jul 25, 2017 at 12:10 PM, Lee Jones <> 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
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()
map->reg_write (drivers/base/regmap/regmap.c:1665) translates to

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;
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.

> drivers/base/regmap/regcache.c:266
> " * Return a negative value on failure, 0 on success."
> I can hardly find this any cleaner than "unspecified".
> > Perhaps we can also change the regmap kerneldoc headers too to match,
> > which might lessen the disparity.
> I'm not familiar with the guts of regmap API, so, I would stick with if (ret < 0)
> for now until documentation specifies positive return values.

 \ /
  Last update: 2017-07-28 02:31    [W:0.057 / U:0.184 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site