linux-kernel - Re: [PATCH v1 3/8] software node: Show properties and their values in sysfs

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Message-ID: <YGHPnkoB/wP6u6HC@smile.fi.intel.com>
Date:   Mon, 29 Mar 2021 16:01:18 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Daniel Scally <djrscally@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Yong Zhi <yong.zhi@...el.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Bingbu Cao <bingbu.cao@...el.com>,
        Tianshu Qiu <tian.shu.qiu@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Subject: Re: [PATCH v1 3/8] software node: Show properties and their values
 in sysfs

On Sun, Mar 28, 2021 at 03:02:24PM +0200, Greg Kroah-Hartman wrote:
> On Sun, Mar 28, 2021 at 03:56:26PM +0300, Andy Shevchenko wrote:
> > On Sun, Mar 28, 2021 at 9:47 AM Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Sun, Mar 28, 2021 at 12:20:07AM +0200, Andy Shevchenko wrote:
> > > > It's very convenient to see what properties and their values
> > > > are currently being assigned in the registered software nodes.
> > > >
> > > > Show properties and their values in sysfs.
> > 
> > ...
> > 
> > > > +             for (i = 0; i < prop->length / sizeof(u8); i++)
> > > > +                     len += sysfs_emit_at(buf, len, "%u,", ((u8 *)pointer)[i]);
> > >
> > > No, sysfs is "one value per file", and that is not what you are showing
> > > here at all :(
> > 
> > It is following: it's a "one value" for property in question,
> > 
> > As we may read in [1]: "...so it is socially acceptable to express an
> > array of values of the same type."
> > 
> > And here is exactly the case: *values of the same type*.
> 
> So what is it going to look like exactly?

Basically we have two approaches (already done in the kernel!) use space or
comma for a separator. So:
 - for boolean it will be an empty string (and it's one value always)
 - for integers it will be, for example, '0,1,2' (w/o single quotes)
   for property array with values 0, 1, and 2
 - for plain integers or arrays out of 1 element it will be plain integer
 - for strings it will be, for example, '"str1","str2"' (w/o single quotes)
   for array of string { "str1", "str2" }
 - for single string or array out of 1 element, it will be '"str"' (w/o single
   quotes)

This should be a part of documentation.

> And what tool is going to be
> there to parse this mess?  Who is going to to use it?

I guess something like hwinfo (needs a patch).

The idea behind that this is following what ACPI and DT provides to the users
via /sys/firmware/ (however, in binary format). I can re-do to provide a
binary, and it will effectively make software nodes in align with the rest.

-- 
With Best Regards,
Andy Shevchenko