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

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

> > > > > +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.

> > > > > + 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?

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