linux-kernel - Re: [PATCH v8 04/10] reset: eyeq5: add platform driver

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Date: Thu, 29 Feb 2024 13:18:08 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: "Andy Shevchenko" <andriy.shevchenko@...el.com>
Cc: "Gregory CLEMENT" <gregory.clement@...tlin.com>, "Michael Turquette"
 <mturquette@...libre.com>, "Stephen Boyd" <sboyd@...nel.org>, "Rob Herring"
 <robh+dt@...nel.org>, "Krzysztof Kozlowski"
 <krzysztof.kozlowski+dt@...aro.org>, "Conor Dooley" <conor+dt@...nel.org>,
 "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>, "Linus Walleij"
 <linus.walleij@...aro.org>, Rafał Miłecki
 <rafal@...ecki.pl>, "Philipp Zabel" <p.zabel@...gutronix.de>, "Vladimir
 Kondratiev" <vladimir.kondratiev@...ileye.com>,
 <linux-mips@...r.kernel.org>, <linux-clk@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Thomas
 Petazzoni" <thomas.petazzoni@...tlin.com>, "Tawfik Bayouk"
 <tawfik.bayouk@...ileye.com>, <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v8 04/10] reset: eyeq5: add platform driver

Hello,

On Thu Feb 29, 2024 at 12:22 PM CET, Andy Shevchenko wrote:
> On Wed, Feb 28, 2024 at 06:04:47PM +0100, Théo 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, Théo Lebrun wrote:
>
> ...
>
> > > > +	u32 offset = id & GENMASK(7, 0);
> > > > +	u32 domain = id >> 8;
> > >
> > > Perhaps
> > >
> > > 	u32 offset = (id & GENMASK(7, 0)) >> 0;
> > > 	u32 domain = (id & GENMASK(31, 8)) >> 8;
> > >
> > > for better understanding the split?
> > 
> > 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 = np;
> > >
> > > It's better to use device_set_node().
> > 
> > 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) code
> 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 += __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,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com