Re: [PATCH v12 04/13] mfd: Add Ingenic TCU driver

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Le jeu. 27 juin 2019 à 11:01, Lee Jones <lee.jones@xxxxxxxxxx> a écrit :
On Thu, 27 Jun 2019, Paul Cercueil wrote:
Le jeu. 27 juin 2019 à 8:58, Lee Jones <lee.jones@xxxxxxxxxx> a écrit :
 > On Wed, 26 Jun 2019, Paul Cercueil wrote:
> > Le mer. 26 juin 2019 à 15:18, Lee Jones <lee.jones@xxxxxxxxxx> a
 > > écrit :
 > >  > On Tue, 21 May 2019, Paul Cercueil wrote:
 > >  >
> > > > This driver will provide a regmap that can be retrieved very
 > > early
 > >  > > in
 > >  > >  the boot process through the API function
 > > ingenic_tcu_get_regmap().
 > >  > >
> > > > Additionally, it will call devm_of_platform_populate() so that
 > > all
 > >  > > the
 > >  > >  children devices will be probed.
 > >  > >
 > >  > >  Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
 > >  > >  ---
 > >  > >
 > >  > >  Notes:
 > >  > >      v12: New patch
 > >  > >
 > >  > >   drivers/mfd/Kconfig             |   8 +++
 > >  > >   drivers/mfd/Makefile            |   1 +
 > >  > >   drivers/mfd/ingenic-tcu.c       | 113
 > >  > > ++++++++++++++++++++++++++++++++
 > >  > >   include/linux/mfd/ingenic-tcu.h |   8 +++
 > >  > >   4 files changed, 130 insertions(+)
 > >  > >   create mode 100644 drivers/mfd/ingenic-tcu.c
 >
 > [...]
 >
> > > > +static struct regmap * __init ingenic_tcu_create_regmap(struct
 > >  > > device_node *np)
 > >  > >  +{
 > >  > >  +	struct resource res;
 > >  > >  +	void __iomem *base;
 > >  > >  +	struct regmap *map;
 > >  > >  +
 > >  > >  +	if (!of_match_node(ingenic_tcu_of_match, np))
 > >  > >  +		return ERR_PTR(-EINVAL);
 >
 > Drop this check.
 >
 > >  > >  +	base = of_io_request_and_map(np, 0, "TCU");
 > >  > >  +	if (IS_ERR(base))
 > >  > >  +		return ERR_PTR(PTR_ERR(base));
 > >  > >  +
 > >  > >  +	map = regmap_init_mmio(NULL, base,
 > > &ingenic_tcu_regmap_config);
 > >  > >  +	if (IS_ERR(map))
 > >  > >  +		goto err_iounmap;
 >
 > Place this inside probe().
 >
 > >  > >  +	return map;
 > >  > >  +
 > >  > >  +err_iounmap:
 > >  > >  +	iounmap(base);
 > >  > >  +	of_address_to_resource(np, 0, &res);
 > >  > >  +	release_mem_region(res.start, resource_size(&res));
 > >  > >  +
 > >  > >  +	return map;
 > >  > >  +}
 > >  >
 > >  > Why does this need to be set-up earlier than probe()?
 > >
 > >  See the explanation below.
 >
 > I think the answer is, it doesn't.
 >
> > > > +static int __init ingenic_tcu_probe(struct platform_device
 > > *pdev)
 > >  > >  +{
 > >  > >  +	struct regmap *map =
 > > ingenic_tcu_get_regmap(pdev->dev.of_node);
 > >  > >  +
 > >  > >  +	platform_set_drvdata(pdev, map);
 > >  > >  +
 > >  > >  +	regmap_attach_dev(&pdev->dev, map,
 > > &ingenic_tcu_regmap_config);
 > >  > >  +
 > >  > >  +	return devm_of_platform_populate(&pdev->dev);
 > >  > >  +}
 > >  > >  +
 > >  > >  +static struct platform_driver ingenic_tcu_driver = {
 > >  > >  +	.driver = {
 > >  > >  +		.name = "ingenic-tcu",
 > >  > >  +		.of_match_table = ingenic_tcu_of_match,
 > >  > >  +	},
 > >  > >  +};
 > >  > >  +
 > >  > >  +static int __init ingenic_tcu_platform_init(void)
 > >  > >  +{
 > >  > >  +	return platform_driver_probe(&ingenic_tcu_driver,
 > >  > >  +				     ingenic_tcu_probe);
 > >  >
 > >  > What?  Why?
 > >
> > The device driver probed here will populate the children devices, > > which will be able to retrieve the pointer to the regmap through
 > >  device_get_regmap(dev->parent).
 >
 > I've never heard of this call.  Where is it?

 dev_get_regmap, in <linux/regmap.h>.

> > The children devices are normal platform drivers that can be probed > > the normal way. These are the PWM driver, the watchdog driver, and
 > > the
> > OST (OS Timer) clocksource driver, all part of the same hardware
 > > block
 > >  (the Timer/Counter Unit or TCU).
 >
 > If they are normal devices, then there is no need to roll your own
 > regmap-getter implementation like this.
 >
 > >  > >  +}
 > >  > >  +subsys_initcall(ingenic_tcu_platform_init);
 > >  > >  +
 > >  > >  +struct regmap * __init ingenic_tcu_get_regmap(struct
 > > device_node
 > >  > > *np)
 > >  > >  +{
 > >  > >  +	if (!tcu_regmap)
 > >  > >  +		tcu_regmap = ingenic_tcu_create_regmap(np);
 > >  > >  +
 > >  > >  +	return tcu_regmap;
 > >  > >  +}
 > >  >
 > >  > This makes me pretty uncomfortable.
 > >  >
 > >  > What calls it?
 > >
> > The TCU IRQ driver (patch [06/13]), clocks driver (patch [05/13]),
 > > and the
> > non-OST clocksource driver (patch [07/13]) all probe very early in
 > > the boot
 > >  process, and share the same devicetree node. They call this
 > > function to get
 > >  a pointer to the regmap.
 >
 > Horrible!
 >
> Instead, you should send it through platform_set_drvdata() and collect
 > it in the child drivers with platform_get_drvdata(dev->parent).

The IRQ, clocks and clocksource driver do NOT have a "struct device" to begin with. They are not platform drivers, and cannot be platform drivers, as they must register so early in the boot process, before "struct device"
 is even a thing.

All they get is a pointer to the same devicetree node. Since all of these have to use the same registers, they need to use a shared regmap, which
 they obtain by calling ingenic_tcu_get_regmap() below.

Then, when this driver's probe gets called, the regmap is retrieved and
 attached to the struct device, and then the children devices will be
probed: the watchdog device, the PWM device, the OST device. These three will retrieve the regmap by calling dev_get_regmap(dev->parent, NULL).

That makes sense.

This explanation certainly belongs in the commit log.

Right.

Can you send your v14, as you intended.  I will re-review it with new
eyes when you do.

Could you review v13 instead? v14 will be a v13 with tiny teeny
non-code fixes (delete some newlines, replace %i with %d, and
convert the documentation from .txt to .rst).

> > > > +bool ingenic_tcu_pwm_can_use_chn(struct device *dev, unsigned
 > > int
 > >  > > channel)
 > >  > >  +{
 > >  > >  +	const struct ingenic_soc_info *soc =
 > >  > > device_get_match_data(dev->parent);
 > >  > >  +
 > >  > >  +	/* Enable all TCU channels for PWM use by default except
 > > channels
 > >  > > 0/1 */
> > > > + u32 pwm_channels_mask = GENMASK(soc->num_channels - 1, 2);
 > >  > >  +
 > >  > >  +	device_property_read_u32(dev->parent,
 > > "ingenic,pwm-channels-mask",
 > >  > >  +				 &pwm_channels_mask);
 >
 > Doesn't this call overwrite the previous assignment above?

Yes, that's intended. You have a default value, that can be overriden
 by a device property.

You should provide a comment here to make your intentions clear.

Ok.

 > >  > >  +	return !!(pwm_channels_mask & BIT(channel));
 > >  > >  +}
 > >  > >  +EXPORT_SYMBOL_GPL(ingenic_tcu_pwm_can_use_chn);
 >
 > Where is this called from?

 This is called from the PWM driver.

Why can't it live in the PWM driver?

It totally can. I'll move it there.


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