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Date: Thu, 27 Jun 2019 11:19:48 +0200
From: Paul Cercueil <paul@...pouillou.net>
To: Lee Jones <lee.jones@...aro.org>
Cc: Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Ralf Baechle <ralf@...ux-mips.org>,
Paul Burton <paul.burton@...s.com>,
James Hogan <jhogan@...nel.org>,
Jonathan Corbet <corbet@....net>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>,
Michael Turquette <mturquette@...libre.com>,
Stephen Boyd <sboyd@...nel.org>,
Jason Cooper <jason@...edaemon.net>,
Marc Zyngier <marc.zyngier@....com>,
Mathieu Malaterre <malat@...ian.org>,
linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
linux-mips@...r.kernel.org, linux-doc@...r.kernel.org,
linux-clk@...r.kernel.org, od@...c.me
Subject: Re: [PATCH v12 04/13] mfd: Add Ingenic TCU driver
Le jeu. 27 juin 2019 à 11:01, Lee Jones <lee.jones@...aro.org> a
écrit :
> On Thu, 27 Jun 2019, Paul Cercueil wrote:
>> Le jeu. 27 juin 2019 à 8:58, Lee Jones <lee.jones@...aro.org> a
>> écrit :
>> > On Wed, 26 Jun 2019, Paul Cercueil wrote:
>> > > Le mer. 26 juin 2019 à 15:18, Lee Jones
>> <lee.jones@...aro.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@...pouillou.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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