linux-kernel - Re: [PATCH net-next v7 8/8] mfd: zl3073x: Register DPLL sub-device during init

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Message-ID: <20250513094126.GF2936510@google.com>
Date: Tue, 13 May 2025 10:41:26 +0100
From: Lee Jones <lee@...nel.org>
To: Ivan Vecera <ivecera@...hat.com>
Cc: Andy Shevchenko <andy.shevchenko@...il.com>, netdev@...r.kernel.org,
	Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
	Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>,
	Jiri Pirko <jiri@...nulli.us>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Prathosh Satish <Prathosh.Satish@...rochip.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Michal Schmidt <mschmidt@...hat.com>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH net-next v7 8/8] mfd: zl3073x: Register DPLL sub-device
 during init

On Mon, 12 May 2025, Ivan Vecera wrote:

> On 07. 05. 25 5:26 odp., Lee Jones wrote:
> > On Wed, 07 May 2025, Andy Shevchenko wrote:
> > 
> > > On Wed, May 07, 2025 at 03:56:37PM +0200, Ivan Vecera wrote:
> > > > On 07. 05. 25 3:41 odp., Andy Shevchenko wrote:
> > > > > On Wed, May 7, 2025 at 3:45 PM Ivan Vecera <ivecera@...hat.com> wrote:
> > > 
> > > ...
> > > 
> > > > > > +static const struct zl3073x_pdata zl3073x_pdata[ZL3073X_MAX_CHANNELS] = {
> > > > > > +       { .channel = 0, },
> > > > > > +       { .channel = 1, },
> > > > > > +       { .channel = 2, },
> > > > > > +       { .channel = 3, },
> > > > > > +       { .channel = 4, },
> > > > > > +};
> > > > > 
> > > > > > +static const struct mfd_cell zl3073x_devs[] = {
> > > > > > +       ZL3073X_CELL("zl3073x-dpll", 0),
> > > > > > +       ZL3073X_CELL("zl3073x-dpll", 1),
> > > > > > +       ZL3073X_CELL("zl3073x-dpll", 2),
> > > > > > +       ZL3073X_CELL("zl3073x-dpll", 3),
> > > > > > +       ZL3073X_CELL("zl3073x-dpll", 4),
> > > > > > +};
> > > > > 
> > > > > > +#define ZL3073X_MAX_CHANNELS   5
> > > > > 
> > > > > Btw, wouldn't be better to keep the above lists synchronised like
> > > > > 
> > > > > 1. Make ZL3073X_CELL() to use indexed variant
> > > > > 
> > > > > [idx] = ...
> > > > > 
> > > > > 2. Define the channel numbers
> > > > > 
> > > > > and use them in both data structures.
> > > > > 
> > > > > ...
> > > > 
> > > > WDYM?
> > > > 
> > > > > OTOH, I'm not sure why we even need this. If this is going to be
> > > > > sequential, can't we make a core to decide which cell will be given
> > > > > which id?
> > > > 
> > > > Just a note that after introduction of PHC sub-driver the array will look
> > > > like:
> > > > static const struct mfd_cell zl3073x_devs[] = {
> > > >         ZL3073X_CELL("zl3073x-dpll", 0),  // DPLL sub-dev for chan 0
> > > >         ZL3073X_CELL("zl3073x-phc", 0),   // PHC sub-dev for chan 0
> > > >         ZL3073X_CELL("zl3073x-dpll", 1),  // ...
> > > >         ZL3073X_CELL("zl3073x-phc", 1),
> > > >         ZL3073X_CELL("zl3073x-dpll", 2),
> > > >         ZL3073X_CELL("zl3073x-phc", 2),
> > > >         ZL3073X_CELL("zl3073x-dpll", 3),
> > > >         ZL3073X_CELL("zl3073x-phc", 3),
> > > >         ZL3073X_CELL("zl3073x-dpll", 4),
> > > >         ZL3073X_CELL("zl3073x-phc", 4),   // PHC sub-dev for chan 4
> > > > };
> > > 
> > > Ah, this is very important piece. Then I mean only this kind of change
> > > 
> > > enum {
> > > 	// this or whatever meaningful names
> > > 	..._CH_0	0
> > > 	..._CH_1	1
> > > 	...
> > > };
> > > 
> > > static const struct zl3073x_pdata zl3073x_pdata[ZL3073X_MAX_CHANNELS] = {
> > >         { .channel = ..._CH_0, },
> > >         ...
> > > };
> > > 
> > > static const struct mfd_cell zl3073x_devs[] = {
> > >         ZL3073X_CELL("zl3073x-dpll", ..._CH_0),
> > >         ZL3073X_CELL("zl3073x-phc", ..._CH_0),
> > >         ...
> > > };
> > 
> > This is getting hectic.  All for a sequential enumeration.  Seeing as
> > there are no other differentiations, why not use IDA in the child
> > instead?
> 
> For that, there have to be two IDAs, one for DPLLs and one for PHCs...

Sorry, can you explain a bit more.  Why is this a problem?

The IDA API is very simple.

Much better than building your own bespoke MACROs.

> The approach in my second reply in this thread is simpler and taken
> in v8.
> 
> <cite>
> +#define ZL3073X_PDATA(_channel)			\
> +	(&(const struct zl3073x_pdata) {	\
> +		.channel = _channel,		\
> +	})
> +
> +#define ZL3073X_CELL(_name, _channel)				\
> +	MFD_CELL_BASIC(_name, NULL, ZL3073X_PDATA(_channel),	\
> +		       sizeof(struct zl3073x_pdata), 0)
> +
> +static const struct mfd_cell zl3073x_devs[] = {
> +	ZL3073X_CELL("zl3073x-dpll", 0),
> +	ZL3073X_CELL("zl3073x-dpll", 1),
> +	ZL3073X_CELL("zl3073x-dpll", 2),
> +	ZL3073X_CELL("zl3073x-dpll", 3),
> +	ZL3073X_CELL("zl3073x-dpll", 4),
> +};
> </cite>
> 
> Lee, WDYT?
> 
> Thanks,
> Ivan
> 

-- 
Lee Jones [李琼斯]