Date:   Tue, 5 Nov 2019 08:11:16 +0000
From:   "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
To:     "mazziesaccount@...il.com" <mazziesaccount@...il.com>,
        "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>,
        "sboyd@...nel.org" <sboyd@...nel.org>
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Subject: Re: [RFC PATCH v2 05/13] clk: bd718x7: Support ROHM BD71828 clk
 block

Hello Stephen,

On Mon, 2019-11-04 at 16:55 -0800, Stephen Boyd wrote:
> Quoting Vaittinen, Matti (2019-10-28 23:28:51)
> > On Mon, 2019-10-28 at 16:32 -0700, Stephen Boyd wrote:
> > > Quoting Matti Vaittinen (2019-10-24 04:44:40)
> > > > diff --git a/drivers/clk/clk-bd718x7.c b/drivers/clk/clk-
> > > > bd718x7.c
> > > > index ae6e5baee330..d17a19e04592 100644
> > > > --- a/drivers/clk/clk-bd718x7.c
> > > > +++ b/drivers/clk/clk-bd718x7.c
> > > > @@ -8,6 +8,7 @@
> > > >  #include <linux/platform_device.h>
> > > >  #include <linux/slab.h>
> > > >  #include <linux/mfd/rohm-bd718x7.h>
> > > > +#include <linux/mfd/rohm-bd71828.h>
> > > >  #include <linux/mfd/rohm-bd70528.h>
> > > 
> > > It would be really great to not need to include these random
> > > header
> > > files in this driver and just use raw numbers somehow. Looks like
> > > maybe
> > > it can be done by populating a different device name from the mfd
> > > driver
> > > depending on the version of the clk controller desired? Then that
> > > can
> > > be
> > > matched in this clk driver and we can just put the register info
> > > in
> > > this
> > > file?
> > 
> > I still like keeping the chip type information on one header - no
> > matter what-ever format the clk-controller type/version information
> > is.
> > Rationale is that MFD and also few other sub-devices (not only the
> > clk)
> > need to use it. Currently at least the RTC.
> > 
> > But if we define clk register information for all PMICs in this c-
> > file, 
> > then (I think) we can only include the <linux/mfd/rohm-generic.h> -
> > which contains the PMIC type defines and the generic MFD data
> > structure. That would:
> > 
> > -#include <linux/mfd/rohm-bd718x7.h>
> > -#include <linux/mfd/rohm-bd71828.h>
> > -#include <linux/mfd/rohm-bd70528.h>
> > +#include <linux/mfd/rohm-generic.h>
> > 
> > That way the chip-type information could still be same for MFD and
> > all
> > sub-devices but clk driver would not need to include all the
> > details
> > for all the PMICs. I understand your point well as clk registers
> > for
> > these PMICs are really *limited*.
> > 
> 
> It's not even just about clk registers. It's also about how we have
> device compatible strings and device names but this driver isn't
> using
> them to differentiate. Instead, it's looking at the parent device. I
> don't get it. Why can't the MFD populate different clk devices for
> the
> different PMICs and make this driver completely oblivious to the
> parent
> device name/structure and these headers?

Probably because I didn't know how MFD/child device 'matching' works.

Do you mean the clk driver could do something like:

static const struct platform_device_id bd718x7_clk_id[] = {
        { "bd71837-clk", FOO},
        { "bd71847-clk", BAR},
        { "bd70528-clk", BAZ},
        { "bd71828-clk", BAF},
        { },
};
MODULE_DEVICE_TABLE(platform, bd718x7_clk_id);

static struct platform_driver bd71837_clk = {
        .driver = {
                .name = "bd718xx-clk",
        },
        .probe = bd71837_clk_probe,
	.id_table = bd718x7_clk_id
};

and then in MFD we just use correct name string for the mfd cell
representing the clk? (Eg. one of the bd71837-clk, bd71847-clk,
bd70528-clk, bd71828-clk) and in clk probe just differentiate based on
FOO, BAR, BAZ and BAF?

I guess we could do that (didn't try it out yet so I only guess for
now) - but I think this don't really mitigate the need for common
header. If we change the sub-device match mechanism to this then the
same mechanism should probably be applied to all sub-devices. And that
would be a case where I would like to see the very same FOO, BAR, BAZ
and BAF being used for all sub-devices - meaning it should still be a
MFD header. I think the drivers/clk/clk-s2mps11.c, drivers/mfd/sec-
core.c and include/linux/mfd/samsung/core.h are examples of this.

But I do like this platform_device_id based PMIC differentiation
better. It looks like the "de facto" way of doing this. Still, as I
said, I don't see we're getting rid of common header this way. Anyways,
I think I can cook-up patches to change this if I get buy-in from Lee,
Alexandre and Mark for changing the existing mechanism.

Thanks for teaching me something new once again! :)

Br,
	Matti Vaittinen

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