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Date: Thu, 29 Feb 2024 13:18:08 +0100
Message-Id: <CZHK1ZCSROM5.X4WYN7SAZJTH@bootlin.com>
From: =?utf-8?q?Th=C3=A9o_Lebrun?= <theo.lebrun@bootlin.com>
Subject: Re: [PATCH v8 04/10] reset: eyeq5: add platform driver
Cc: "Gregory CLEMENT" <gregory.clement@bootlin.com>, "Michael Turquette"
 <mturquette@baylibre.com>, "Stephen Boyd" <sboyd@kernel.org>, "Rob Herring"
 <robh+dt@kernel.org>, "Krzysztof Kozlowski"
 <krzysztof.kozlowski+dt@linaro.org>, "Conor Dooley" <conor+dt@kernel.org>,
 "Thomas Bogendoerfer" <tsbogend@alpha.franken.de>, "Linus Walleij"
 <linus.walleij@linaro.org>, =?utf-8?q?Rafa=C5=82_Mi=C5=82ecki?=
 <rafal@milecki.pl>, "Philipp Zabel" <p.zabel@pengutronix.de>, "Vladimir
 Kondratiev" <vladimir.kondratiev@mobileye.com>,
 <linux-mips@vger.kernel.org>, <linux-clk@vger.kernel.org>,
 <devicetree@vger.kernel.org>, <linux-kernel@vger.kernel.org>, "Thomas
 Petazzoni" <thomas.petazzoni@bootlin.com>, "Tawfik Bayouk"
 <tawfik.bayouk@mobileye.com>, <linux-gpio@vger.kernel.org>
To: "Andy Shevchenko" <andriy.shevchenko@intel.com>
References: <20240227-mbly-clk-v8-0-c57fbda7664a@bootlin.com>
 <20240227-mbly-clk-v8-4-c57fbda7664a@bootlin.com>
 <Zd4bbCsY54XEnvJM@smile.fi.intel.com>
 <CZGVIWR4H4DE.3M5H3H99X0QPT@bootlin.com>
 <ZeBo4N204gLO0eUd@smile.fi.intel.com>
In-Reply-To: <ZeBo4N204gLO0eUd@smile.fi.intel.com>

Hello,

On Thu Feb 29, 2024 at 12:22 PM CET, Andy Shevchenko wrote:
> On Wed, Feb 28, 2024 at 06:04:47PM +0100, Th=C3=A9o Lebrun wrote:
> > On Tue Feb 27, 2024 at 6:27 PM CET, Andy Shevchenko wrote:
> > > On Tue, Feb 27, 2024 at 03:55:25PM +0100, Th=C3=A9o Lebrun wrote:
>
> ...
>
> > > > +	u32 offset =3D id & GENMASK(7, 0);
> > > > +	u32 domain =3D id >> 8;
> > >
> > > Perhaps
> > >
> > > 	u32 offset =3D (id & GENMASK(7, 0)) >> 0;
> > > 	u32 domain =3D (id & GENMASK(31, 8)) >> 8;
> > >
> > > for better understanding the split?
> >=20
> > Do the additional zero-bit-shift and GENMASK() help understanding? My
> > brain needs time to parse them to then notice they do nothing and
> > simplify the code in my head, back to the original version.
>
> In my opinion yes, as you exactly showing the split.
> But. The better is to use FIELD_GET().

I'll go with the FIELD_GET() option!

[...]

>
> > > > +	priv->rcdev.of_node =3D np;
> > >
> > > It's better to use device_set_node().
> >=20
> > I don't see how device_set_node() can help? It works on struct device
> > pointers. Here priv->rcdev is a reset_controller_dev struct. There are
> > no users of device_set_node() in drivers/reset/.
>
> No users doesn't mean it's good. The API is relatively "new" and takes
> care of two things:
> 1) it uses agnostic interface;
> 2) it doesn't require any firmware node direct dereference.
>
> The 2) is most important here as allows us to refactor (firmware node) co=
de
> in the future.

I think I get the point of device_set_node(). I still do not understand
how it could help me fill the ->of_node field in a reset_controller_dev
structure?

Should I be using device_set_node() to fill the struct device pointer
and the reset subsystem, by some magic, will pick this up and use it
for its own of_node field? I've not seen any magic/code doing that.

[...]

> > > > +		priv->rcdev.nr_resets +=3D __builtin_popcount(eq5r_valid_masks[i=
]);
> > >
> > > Please, use corresponding hweightXX() API.
> >
> > Noted. I did not find this keyword even though I searched quite a bit
> > for it. "popcount" sounds more logical to me. :-)
>
> Hmm... But it's fundamental, it's called Hamming weight.
> https://en.wikipedia.org/wiki/Hamming_weight

Makes sense now. I've always called it population count following the
name of the matching instruction on x86 (and I believe other ISAs). TIL.

Regards,

--
Th=C3=A9o Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com