linux-kernel - Re: [PATCH v2] meson saradc: add iio device attrib to switch channel 7 mux

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Date:   Tue, 30 May 2023 02:32:58 +0300
From:   andy.shevchenko@...il.com
To:     George Stark <gnstark@...rdevices.ru>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "jic23@...nel.org" <jic23@...nel.org>,
        "lars@...afoo.de" <lars@...afoo.de>,
        "neil.armstrong@...aro.org" <neil.armstrong@...aro.org>,
        "khilman@...libre.com" <khilman@...libre.com>,
        "jbrunet@...libre.com" <jbrunet@...libre.com>,
        "martin.blumenstingl@...glemail.com" 
        <martin.blumenstingl@...glemail.com>,
        "nuno.sa@...log.com" <nuno.sa@...log.com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-amlogic@...ts.infradead.org" 
        <linux-amlogic@...ts.infradead.org>, kernel <kernel@...rdevices.ru>
Subject: Re: [PATCH v2] meson saradc: add iio device attrib to switch channel
 7 mux

Mon, May 29, 2023 at 01:31:40AM +0300, George Stark kirjoitti:
> On 5/28/23 13:46, Andy Shevchenko wrote:
> > On Sun, May 28, 2023 at 12:48:54AM +0300, George Stark wrote:

...

> > > +	if (index >= ARRAY_SIZE(chan7_vol))
> > > +		index = ARRAY_SIZE(chan7_vol) - 1;
> > I think this is incorrect and prone to error in the future in case this array
> > will be extended. What I would expect is to return something like "unknown".
> 
> I agree this part is unclean. Actually the register's last 3 (out of 8)
> possible values are stand for the same mux input "ch7_input". So
> theoretically we can read from register a value out of array bounds. There
> should be a comment at least.

You can add there in the array to extend it up to 8 entries, so it will be
clear. And for the rest you will return unknown / unsupported / etc.

...

> > > +static const char * const chan7_vol[] = {
> > > +	"gnd",
> > > +	"vdd/4",
> > > +	"vdd/2",
> > > +	"vdd*3/4",
> > > +	"vdd",
> > > +	"ch7_input",
> > > +};

> About the question of naming mux inputs from the other letter (vdd/2 vs
> 0.5Vdd etc).
> While I fully agree with you that point is better than slash but mixing
> letter cases... should we?

What's wrong with that?

> e.g. this is how iio_info output looks like now:
> ...
>             voltage7:  (input)
>             3 channel-specific attributes found:
>                 attr  0: mean_raw value: 0
>                 attr  1: raw value: 1
>                 attr  2: scale value: 0.439453125
>         4 device-specific attributes found:
>                 attr  0: chan7_mux value: gnd
>                 attr  1: chan7_mux_available value: gnd vdd/4 vdd/2 vdd*3/4
> vdd ch7_input
>                 attr  2: current_timestamp_clock value: realtime
> 
>                 attr  3: waiting_for_supplier value: 0
> 
> or naming with Jonathan's approach
> /sys/devices/platform/soc/fe000000.bus/fe002c00.adc/iio:device0/in_voltage_0.5vdd_raw

See the alternative I proposed is to have _ delimiter. But that might make
parsing a bit harder in user space.

-- 
With Best Regards,
Andy Shevchenko