linux-kernel - Re: [PATCH net-next v6 8/8] mfd: zl3073x: Register DPLL sub-device during init

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Message-ID: <20250507110621.GJ3865826@google.com>
Date: Wed, 7 May 2025 12:06:21 +0100
From: Lee Jones <lee@...nel.org>
To: Ivan Vecera <ivecera@...hat.com>
Cc: 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>, Andy Shevchenko <andy@...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 v6 8/8] mfd: zl3073x: Register DPLL sub-device
 during init

On Fri, 02 May 2025, Ivan Vecera wrote:

> 
> 
> On 01. 05. 25 3:22 odp., Lee Jones wrote:
> > On Wed, 30 Apr 2025, Ivan Vecera wrote:
> > 
> > > Register DPLL sub-devices to expose the functionality provided
> > > by ZL3073x chip family. Each sub-device represents one of
> > > the available DPLL channels.
> > > 
> > > Signed-off-by: Ivan Vecera <ivecera@...hat.com>
> > > ---
> > > v4->v6:
> > > * no change
> > > v3->v4:
> > > * use static mfd cells
> > > ---
> > >   drivers/mfd/zl3073x-core.c | 19 +++++++++++++++++++
> > >   1 file changed, 19 insertions(+)
> > > 
> > > diff --git a/drivers/mfd/zl3073x-core.c b/drivers/mfd/zl3073x-core.c
> > > index 050dc57c90c3..3e665cdf228f 100644
> > > --- a/drivers/mfd/zl3073x-core.c
> > > +++ b/drivers/mfd/zl3073x-core.c
> > > @@ -7,6 +7,7 @@
> > >   #include <linux/device.h>
> > >   #include <linux/export.h>
> > >   #include <linux/math64.h>
> > > +#include <linux/mfd/core.h>
> > >   #include <linux/mfd/zl3073x.h>
> > >   #include <linux/module.h>
> > >   #include <linux/netlink.h>
> > > @@ -755,6 +756,14 @@ static void zl3073x_devlink_unregister(void *ptr)
> > >   	devlink_unregister(ptr);
> > >   }
> > > +static const struct mfd_cell zl3073x_dpll_cells[] = {
> > > +	MFD_CELL_BASIC("zl3073x-dpll", NULL, NULL, 0, 0),
> > > +	MFD_CELL_BASIC("zl3073x-dpll", NULL, NULL, 0, 1),
> > > +	MFD_CELL_BASIC("zl3073x-dpll", NULL, NULL, 0, 2),
> > > +	MFD_CELL_BASIC("zl3073x-dpll", NULL, NULL, 0, 3),
> > > +	MFD_CELL_BASIC("zl3073x-dpll", NULL, NULL, 0, 4),
> > > +};
> > 
> > What other devices / subsystems will be involved when this is finished?
> 
> Lee, btw. I noticed from another discussion that you mentioned that
> mfd_cell->id should not be used outside MFD.
> 
> My sub-drivers uses this to get DPLL channel number that should be used
> for the particular sub-device.
> 
> E.g.
> 1) MFD_CELL_BASIC("zl3073x-dpll", NULL, NULL, 0, 2);
> 2) MFD_CELL_BASIC("zl3073x-phc", NULL, NULL, 0, 3);
> 
> In these cases dpll_zl3073x sub-driver will use DPLL channel 2 for this
> DPLL sub-device and ptp_zl3073x sub-driver will use DPLL channel 3 for
> this PHC sub-device.
> 
> platform_device->id cannot be used for this purpose in conjunction with
> PLATFORM_DEVID_AUTO as that ->id can be arbitrary.
> 
> So if I cannot use mfd_cell->id what should I use for that case?
> Platform data per cell with e.g. the DPLL channel number?

Yes, using the device ID for anything other than enumeration is a hack.

Channel numbers and the like should be passed as platform data.

-- 
Lee Jones [李琼斯]