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


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).

>> > > +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.

>> > > + 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.

> I think this needs a review by the DT guys.

Rob already acked the bindings, which describe this property.

>> > > diff --git a/include/linux/mfd/ingenic-tcu.h
>> > > b/include/linux/mfd/ingenic-tcu.h
>> > > index 2083fa20821d..21df23916cd2 100644
>> > > --- a/include/linux/mfd/ingenic-tcu.h
>> > > +++ b/include/linux/mfd/ingenic-tcu.h
>> > > @@ -6,6 +6,11 @@
>> > > #define __LINUX_MFD_INGENIC_TCU_H_
>> > >
>> > > #include <linux/bitops.h>
>> > > +#include <linux/init.h>
>> > > +
>> > > +struct device;
>> > > +struct device_node;
>> > > +struct regmap;
>> > >
>> > > #define TCU_REG_WDT_TDR 0x00
>> > > #define TCU_REG_WDT_TCER 0x04
>> > > @@ -53,4 +58,7 @@
>> > > #define TCU_REG_TCNTc(c) (TCU_REG_TCNT0 + ((c) *
>> > > TCU_CHANNEL_STRIDE))
>> > > #define TCU_REG_TCSRc(c) (TCU_REG_TCSR0 + ((c) *
>> > > TCU_CHANNEL_STRIDE))
>> > >
>> > > +struct regmap * __init ingenic_tcu_get_regmap(struct
>> device_node
>> > > *np);
>> > > +bool ingenic_tcu_pwm_can_use_chn(struct device *dev, unsigned
>> int
>> > > channel);
>> > > +
>> > > #endif /* __LINUX_MFD_INGENIC_TCU_H_ */
>> >
>>
>>
>
> --
> Lee Jones [李琼斯]
> Linaro Services Technical Lead
> Linaro.org │ Open source software for ARM SoCs
> Follow Linaro: Facebook | Twitter | Blog


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