linux-kernel - Re: [PATCH v1] mfd: Add support for Merrifield Basin Cove PMIC

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Date:   Thu, 4 Apr 2019 10:03:14 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mfd: Add support for Merrifield Basin Cove PMIC

On Thu, 04 Apr 2019, Andy Shevchenko wrote:

> On Thu, Apr 04, 2019 at 08:03:57AM +0100, Lee Jones wrote:
> > On Thu, 04 Apr 2019, Lee Jones wrote:
> > > On Tue, 02 Apr 2019, Andy Shevchenko wrote:
> > > > On Tue, Apr 02, 2019 at 06:12:11AM +0100, Lee Jones wrote:
> > > > > On Mon, 18 Mar 2019, Andy Shevchenko wrote:
> 
> > > > > > +static const struct mfd_cell bcove_dev[] = {
> > > > > > +	{
> > > > > > +		.name = "mrfld_bcove_pwrbtn",
> > > > > > +		.num_resources = 1,
> > > > > > +		.resources = &irq_level2_resources[0],
> > > > > > +	}, {
> > > > > > +		.name = "mrfld_bcove_tmu",
> > > > > > +		.num_resources = 1,
> > > > > > +		.resources = &irq_level2_resources[1],
> > > > > > +	}, {
> > > > > > +		.name = "mrfld_bcove_thermal",
> > > > > > +		.num_resources = 1,
> > > > > > +		.resources = &irq_level2_resources[2],
> > > > > > +	}, {
> > > > > > +		.name = "mrfld_bcove_bcu",
> > > > > > +		.num_resources = 1,
> > > > > > +		.resources = &irq_level2_resources[3],
> > > > > > +	}, {
> > > > > > +		.name = "mrfld_bcove_adc",
> > > > > > +		.num_resources = 1,
> > > > > > +		.resources = &irq_level2_resources[4],
> > > > > > +	}, {
> > > > > > +		.name = "mrfld_bcove_charger",
> > > > > > +		.num_resources = 1,
> > > > > > +		.resources = &irq_level2_resources[5],
> > > > > > +	}, {
> > > > > > +		.name = "mrfld_bcove_extcon",
> > > > > > +		.num_resources = 1,
> > > > > > +		.resources = &irq_level2_resources[5],
> > > > > > +	}, {
> > > > > > +		.name = "mrfld_bcove_gpio",
> > > > > > +		.num_resources = 1,
> > > > > > +		.resources = &irq_level2_resources[6],
> > > > > > +	},
> > > > > > +	{	.name = "mrfld_bcove_region", },
> > > > > > +};
> 
> > > > > > +	for (i = 0; i < ARRAY_SIZE(irq_level2_resources); i++) {
> > > > > > +		ret = platform_get_irq(pdev, i);
> > > > > > +		if (ret < 0)
> > > > > > +			return ret;
> > > > > > +
> > > > > > +		irq_level2_resources[i].start = ret;
> > > > > > +		irq_level2_resources[i].end = ret;
> > > > > > +	}
> > > > > 
> > > > > Although succinct, dragging values from one platform device into
> > > > > another doesn't sound that neat.
> > > > 
> > > > So, how to split resources given in one _physical_ multi-functional device to
> > > > several of them?  Isn't it what MFD framework for?
> > > > 
> > > > Any other approach here? I'm all ears!
> > > 
> > > From the child:
> > > 
> > >   platform_get_irq(dev->parent, CLIENT_ID);
> 
> So, instead of keeping a fragile approach in one driver, we will spread this
> to all of them.

No, the fragileness goes away with implicit definitions of IDs.

> > If you set the .id of the cell properly you could do:
> > 
> >   platform_get_irq(dev->parent, dev->id);
> 
> This will bring a confuse, ID is used to form an instance name, for now
> we don't have several instances of any of the devices from PMIC.

That is true.  It is probably an abuse of the API. :)

I'm just floating ideas.

> On top of above, some of the resources (one already, others might be a case in
> the future) is split between two drivers, which would bring even more confusion
> to the entire picture.

I don't see any indication in the code that 2 platform devices can't
share the same .id value.  But again, this is probably academic since
abusing the API should probably be avoided in general.

> > > > > Also, since the ordering of the
> > > > > devices is critical in this implementation, it also comes across as
> > > > > fragile.
> > > > 
> > > > How fragile? In ACPI we don't have IRQ labeling scheme. Index is used for that.
> > > > 
> > > > > Any reason why ACPI can't register all of the child devices, or for
> > > > > the child devices to obtain their IRQ directly from the tables?
> > > > 
> > > > And how are we supposed to enumerated them taking into consideration single
> > > > ACPI ID given?
> > > 
> > > This question was a little whimsical, since I have no idea how the
> > > ACPI tables you're working with are laid out.
> 
> There is one device node with several IRQ and other resources.
> In pseudo code:
> 
> 	device node {
> 		device ID,
> 		IRQ 0,
> 		IRQ 1,
> 		...
> 		MMIO 0,
> 		...
> 	}

Sure.  Thanks for the explanation.

Very well.  I guess it's not too bad as it is.

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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