linux-kernel - Re: [PATCH v3 08/17] clk: eyeq5: add platform driver

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Message-Id: <CYN33YJ10HYS.2YDXB158LFZPL@bootlin.com>
Date: Wed, 24 Jan 2024 17:41:25 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: "Krzysztof Kozlowski" <krzysztof.kozlowski@...aro.org>, "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>
Cc: "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 v3 08/17] clk: eyeq5: add platform driver

Hello,

On Wed Jan 24, 2024 at 8:05 AM CET, Krzysztof Kozlowski wrote:
> On 23/01/2024 19:46, Théo Lebrun wrote:
> > Add the Mobileye EyeQ5 clock controller driver. It might grow to add
> > support for other platforms from Mobileye.
> > 
> > It handles 10 read-only PLLs derived from the main crystal on board. It
> > exposes a table-based divider clock used for OSPI. Other platform
> > clocks are not configurable and therefore kept as fixed-factor
> > devicetree nodes.
> > 
> > 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.
> > 
>
>
> > +#define OLB_PCSR1_RESET				BIT(0)
> > +#define OLB_PCSR1_SSGC_DIV			GENMASK(4, 1)
> > +/* Spread amplitude (% = 0.1 * SPREAD[4:0]) */
> > +#define OLB_PCSR1_SPREAD			GENMASK(9, 5)
> > +#define OLB_PCSR1_DIS_SSCG			BIT(10)
> > +/* Down-spread or center-spread */
> > +#define OLB_PCSR1_DOWN_SPREAD			BIT(11)
> > +#define OLB_PCSR1_FRAC_IN			GENMASK(31, 12)
> > +
> > +static struct clk_hw_onecell_data *eq5c_clk_data;
> > +static struct regmap *eq5c_olb;
>
> Drop these two. No file-scope regmaps for drivers. Use private container
> structures.

I wouldn't know how to handle the two steps then. Two clocks and the clk
provider are registered at of_clk_init() using CLK_OF_DECLARE_DRIVER().
The rest is at platform device probe. Without a static, there are no
way to pass the struct clk_hw_onecell_data from one to the other.

I've looked at all clock drivers that do CLK_OF_DECLARE_DRIVER() and
register a platform driver.

 - The following use a static variable:
   drivers/clk/axis/clk-artpec6.c
   drivers/clk/clk-aspeed.c
   drivers/clk/clk-ast2600.c
   drivers/clk/clk-eyeq5.c
   drivers/clk/clk-gemini.c
   drivers/clk/clk-milbeaut.c
   drivers/clk/mediatek/clk-mt2701.c
   drivers/clk/mediatek/clk-mt6797.c
   drivers/clk/mediatek/clk-mt8173-infracfg.c
   drivers/clk/nxp/clk-lpc18xx-creg.c
   drivers/clk/ralink/clk-mt7621.c
   drivers/clk/ralink/clk-mtmips.c
   drivers/clk/sunxi/clk-mod0.c
   drivers/clk/axis/clk-artpec6.c

 - Those two declare different clock providers at init and probe:
   drivers/clk/ralink/clk-mt7621.c
   drivers/clk/sunxi/clk-mod0.c

 - It doesn't register new clocks at probe (only resets) so no need to
   share variables.
   drivers/clk/ralink/clk-mtmips.c

>
> ...
>
> > +static void __init eq5c_init(struct device_node *np)
> > +{
> > +	struct device_node *parent_np = of_get_parent(np);
> > +	int i, ret;
> > +
> > +	eq5c_clk_data = kzalloc(struct_size(eq5c_clk_data, hws, EQ5C_NB_CLKS),
> > +				GFP_KERNEL);
> > +	if (!eq5c_clk_data) {
> > +		ret = -ENOMEM;
> > +		goto err;
> > +	}
> > +
> > +	eq5c_clk_data->num = EQ5C_NB_CLKS;
> > +
> > +	/*
> > +	 * Mark all clocks as deferred. We register some now and others at
> > +	 * platform device probe.
> > +	 */
> > +	for (i = 0; i < EQ5C_NB_CLKS; i++)
> > +		eq5c_clk_data->hws[i] = ERR_PTR(-EPROBE_DEFER);
> > +
> > +	/*
> > +	 * Currently, if OLB is not available, we log an error, fail init then
>
> How it could be not available? Only with broken initcall ordering. Fix
> your initcall ordering and then simplify all this weird code.

of_syscon_register() and regmap_init_mmio() lists many reasons for
it to not be available. Am I missing something?

Thanks,

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