linux-kernel - Re: [PATCH v8 03/10] clk: eyeq5: add platform driver, and init routine at of_clk

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Message-ID: <ZeCbvgWY6x1o17Kq@smile.fi.intel.com>
Date: Thu, 29 Feb 2024 16:59:10 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Théo Lebrun <theo.lebrun@...tlin.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 03/10] clk: eyeq5: add platform driver, and init
 routine at of_clk_init()

On Thu, Feb 29, 2024 at 03:27:01PM +0100, Théo Lebrun wrote:
> On Wed, Feb 28, 2024 at 03:33:29PM +0100, Théo Lebrun wrote:
> > On Tue Feb 27, 2024 at 6:11 PM CET, Andy Shevchenko wrote:
> > > On Tue, Feb 27, 2024 at 03:55:24PM +0100, Théo Lebrun wrote:

[...]

> > > > > +	u32		reg;	/* next 8 bytes are r0 and r1 */
> > > >
> > > > Not sure this comments gives any clarification to a mere reader of the code.
> > > > Perhaps you want to name this as reg64 (at least it will show that you have
> > > > 8 bytes, but I have no clue what is the semantic relationship between r0 and
> > > > r1, it's quite cryptic to me). Or maybe it should be reg_0_1?
> > > 
> > > Clocks are defined by two 32-bit registers. We only store the first
> > > register offset because they always follow each other.
> >
> > > I like the reg64 name and will remove the comment. This straight forward
> > > code is found in the rest of the code, I don't think it is anything
> > > hard to understand (ie does not need a comment):
> > > 
> > > 	u32 r0 = readl(base_plls + pll->reg);
> > > 	u32 r1 = readl(base_plls + pll->reg + sizeof(r0));
> >
> > Btw, why readq()/writeq() (with probably the inclusion of io-64-nonatomic-lo-hi.h)
> > can be used in this case? It will be much better overall and be aligned with
> > reg64 name.
> 
> The doc talks in terms of 32-bit registers. I do not see a reason to
> work in 64-bit. If we get a 64-bit value that we need to split we need
> to think about the endianness of our platform, which makes things more
> complex than just reading both values independently.

1) Would be nice to test on the real HW to confirm it doesn't accept 64-bit IO.
2) Still I see a benefit from using lo_hi_readq() and friends directly.

[...]

> > > > I didn't get. If eq5c_init() was finished successfully, why do you need to
> > > > seems repeat what it already done? What did I miss?
> > > 
> > > The key here is that eq5c_init() iterates on eq5c_early_plls[] while
> > > eq5c_probe() iterates on eq5c_plls[]. I've tried to hint at this in the
> > > commit message:
> > > 
> > > > Two PLLs are required early on and are therefore registered at
> > > > of_clk_init(). Those are pll-cpu for the GIC timer and pll-per for the
> > > > UARTs.
> > > 
> > > Doing everything in eq5c_init() is not clean because we expect all new
> > > clock provider drivers to be standard platform drivers. Doing
> > > everything from a platform driver probe doesn't work because some
> > > clocks are required earlier than platform bus init. We therefore do a
> > > mix.
> >
> > Am I missing something or these two pieces are using the same IO resources?
> > This looks like a lot of code duplication without clear benefit. Perhaps
> > you can have a helper?
> 
> There are two subtle differences that make creating a helper difficult:
> 
>  - Logging, pr_*() vs dev_*(). Second option is preferred but only
>    available once a device is created.

Some code uses (yeah, arguable that it's better, but depends on how much
the real deduplication takes)

	if (dev)
		dev_*(...);
	else
		pr_*(...);

>  - Behavior on error: we stop the world for early clocks but keep going
>    for normal clocks.

..(..., bool skip_errors)
{
	...
}

(with the same caveat)?

-- 
With Best Regards,
Andy Shevchenko