linux-kernel - Re: [PATCH v2 1/3] software node: implement reference properties

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Message-ID: <20190907171251.GL2680@smile.fi.intel.com>
Date:   Sat, 7 Sep 2019 20:12:51 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v2 1/3] software node: implement reference properties

On Sat, Sep 07, 2019 at 09:32:40AM -0700, Dmitry Torokhov wrote:
> On Sat, Sep 07, 2019 at 07:08:19PM +0300, Andy Shevchenko wrote:
> > On Fri, Sep 06, 2019 at 03:26:09PM -0700, Dmitry Torokhov wrote:

> > > +	} else if (src->type == DEV_PROP_REF) {
> > > +		/* All reference properties must be arrays */
> > > +		return -EINVAL;
> > 
> > Hmm... What about to duplicate pointer under value union and use is_array to
> > distinguish which one to use? Because...
> 
> Then we have to special-case copying this entry, similar to the pains we
> are going with the strings.

I can't see it as a pain. Simple do the same kmemdup() for the case when
is_array = false and DEV_TYPE_REF?

By the way, don't we need to update property_entry_{get,set}_pointer()?

> > > +	.is_array = true,						\
> > 
> > I really don't like this "cheating".
> 
> This is not cheating. Any single value can be represented as an array of
> one element. Actually, the only reason we have this "is_array" business
> is because for scalar values and short strings it is much cheaper to
> store single value in-line instead of out of line + pointer, especially
> on 64 bit arches.

Yes, and this is a lot of benefit!

> If you want we can change is_array into is_inline.

Nope, is_array is exactly what it tells us about the content. Its functional
load is to distinguish which union (value vs. pointer) we are using.

-- 
With Best Regards,
Andy Shevchenko