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

[Paul Cercueil <paul@crapouillou.net>]

Le jeu. 27 juin 2019 à 11:01, Lee Jones <lee.jones@linaro.org> a 
écrit :
> On Thu, 27 Jun 2019, Paul Cercueil wrote:
>>  Le jeu. 27 juin 2019 à 8:58, Lee Jones <lee.jones@linaro.org> a 
>> écrit :
>>  > On Wed, 26 Jun 2019, Paul Cercueil wrote:
>>  > >  Le mer. 26 juin 2019 à 15:18, Lee Jones 
>> <lee.jones@linaro.org> 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@crapouillou.net>
>>  > >  > >  ---
>>  > >  > >
>>  > >  > >  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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