linux-kernel - Re: [PATCH v4 05/10] mfd: max77650: new core mfd driver

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Date:   Wed, 13 Feb 2019 10:35:45 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>,
        Sebastian Reichel <sre@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Input <linux-input@...r.kernel.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v4 05/10] mfd: max77650: new core mfd driver

śr., 13 lut 2019 o 10:25 Lee Jones <lee.jones@...aro.org> napisał(a):
>
> On Tue, 12 Feb 2019, Lee Jones wrote:
>
> > On Tue, 12 Feb 2019, Bartosz Golaszewski wrote:
> >
> > > wt., 12 lut 2019 o 12:14 Lee Jones <lee.jones@...aro.org> napisał(a):
> > > >
> > > > On Tue, 12 Feb 2019, Bartosz Golaszewski wrote:
> > > >
> > > > > wt., 12 lut 2019 o 11:18 Lee Jones <lee.jones@...aro.org> napisał(a):
> > > > > >
> > > > > > On Tue, 12 Feb 2019, Bartosz Golaszewski wrote:
> > > > > >
> > > > > > > wt., 12 lut 2019 o 10:55 Lee Jones <lee.jones@...aro.org> napisał(a):
> > > > > > > >
> > > > > > > >  * The declaration of a superfluous struct
> > > > > > > >  * 100 lines of additional/avoidable code
> > > > > > > >  * Hacky hoop jumping trying to fudge VIRQs into resources
> > > > > > > >  * Resources were designed for HWIRQs (unless a domain is present)
> > > > > > > >  * Loads of additional/avoidable CPU cycles setting all this up
> > > > > > >
> > > > > > > While the above may be right, this one is negligible and you know it. :)
> > > > > >
> > > > > > You have nested for() loops.  You *are* wasting lots of cycles.
> > > > > >
> > > > > > > > Need I go on? :)
> > > > > > > >
> > > > > > > > Surely the fact that you are using both sides of an API
> > > > > > > > (devm_regmap_init_i2c and regmap_irq_get_*) in the same driver, must
> > > > > > > > set some alarm bells ringing?
> > > > > > > >
> > > > > > > > This whole HWIRQ setting, VIRQ getting, resource hacking is a mess.
> > > > > > > >
> > > > > > > > And for what?  To avoid passing IRQ data to a child driver?
> > > > > > >
> > > > > > > What do you propose? Should I go back to the approach in v1 and pass
> > > > > > > the regmap_irq_chip_data to child drivers?
> > > > > >
> > > > > > I'm saying you should remove all of this hackery and pass IRQs as they
> > > > > > are supposed to be passed (like everyone else does).
> > > > >
> > > > > I'm not sure what you mean by "like everyone else does" - different
> > > > > mfd drivers seem to be doing different things. Is a simple struct
> > > > > containing virtual irq numbers passed to sub-drivers fine?
> > > >
> > > > How do you plan on deriving the VIRQs to place into the struct?
> > >
> > > Exampe:
> > >
> > > struct max77650_gpio_pdata {
> > >     int gpi_irq;
> > > };
> > >
> > > In MFD driver:
> > >
> > > struct max77650_gpio_pdata *gpio_data = devm_kmalloc(dev, sizeof(*gpio_data));
> > >
> > > gpio_data->gpi_irq = regmap_irq_get_virq(irqchip_data, GPI_NUM);
> > >
> > > gpio_cell.platform_data = gpio_data;
> > >
> > > In GPIO driver:
> > >
> > > struct max77650_gpio_pdata *gpio_data = pdev->dev.platform_data;
> > >
> > > int irq = gpio_data->gpi_irq;
> >
> > Definitely not.  What you're trying to do is a hack.
> >
> > If you're using Regmap to handle your IRQs, then you should use Regmap
> > in the client to pull them out.  Setting them via Regmap, then pulling
> > them out again in the *same driver*, only to store them in platform
> > data to be passed to a child device is bonkers.
> >
> > *Either* use the MFD provided platform-data helpers *or* pass and
> > handle them via the Regmap APIs, *not* both.
>
> Right, a plan has been formed.
>
> Hopefully this works and you can avoid all this dancing around.
>
> Firstly, you need to make a small change to:
>
>   drivers/base/regmap/regmap-irq.c
>
> Add the following function:
>
>   struct irq_domain *regmap_irq_get_domain(struct regmap *map)
>

We already do have such function and a lot of mfd drivers actually use it.

> As you can see, it will return the IRQ Domain for the chip.
>
> You can then pass this IRQ domain to mfd_add_devices() and it will do
> the HWIRQ => VIRQ mapping for you on the fly.  Meaning that you can
> remove all the nastiness in max77650_setup_irqs() and have the Input
> device use the standard (e.g. platform_get_irq()) APIs.
>
> How does that Sound?
>

This does sound better! Why didn't you lead with that in the first place?

It's a pity it's not documented, I had to look at the code to find out
irq resources would get translated in mfd_add_devices() if a domain is
present.

In that case - I really don't see a reason to create a superfluous
structure to only hold the main regmap - we can very well get it from
the parent device in sub-drivers as I do now.

Thanks,
Bartosz