linux-kernel - Re: [RFC PATCH 0/6] leds: Fix pca955x GPIO pin mappings

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Date:   Tue, 3 Aug 2021 13:33:38 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Andrew Jeffery <andrew@...id.au>
Cc:     "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        Cédric Le Goater <clg@...d.org>,
        Rob Herring <robh+dt@...nel.org>,
        Joel Stanley <joel@....id.au>, Pavel Machek <pavel@....cz>,
        Linus Walleij <linus.walleij@...aro.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/6] leds: Fix pca955x GPIO pin mappings

On Tue, Aug 3, 2021 at 7:07 AM Andrew Jeffery <andrew@...id.au> wrote:
> On Thu, 29 Jul 2021, at 17:10, Andy Shevchenko wrote:
> > On Thu, Jul 29, 2021 at 3:39 AM Andrew Jeffery <andrew@...id.au> wrote:
> > > On Wed, 28 Jul 2021, at 18:43, Andy Shevchenko wrote:
> > > > On Wed, Jul 28, 2021 at 8:43 AM Andrew Jeffery <andrew@...id.au> wrote:
> > > > > However, userspace would never have
> > > > > got the results it expected with the existing driver implementation, so
> > > > > I guess you could argue that no such (useful) userspace exists. Given
> > > > > that, we could adopt the strategy of always defining a gpiochip
> > > > > covering the whole pin space, and parts of the devicetree binding just
> > > > > become redundant.
> > > >
> > > > I'm lost now. GPIO has its own userspace ABI, how does it work right
> > > > now in application to this chip?
> > >
> > > As above, it "works" if the GPIOs specified in the devicetree are
> > > contiguous from line 0. It's broken if they're not.
> >
> > So, "it never works" means there is no bug. Now, what we need is to
> > keep the same enumeration scheme, but if you wish to be used half/half
> > (or any other ratio), the driver should do like the above mentioned
> > PWM, i.e. register entire space and depending on the requestor either
> > proceed with a line or mark it as BUSY.
> >
> > Ideally, looking into what the chip can do, this should be indeed
> > converted to some like pin control + PWM + LED + GPIO drivers. Then
> > the function in pin mux configuration can show what exactly is enabled
> > on the certain line(s).
>
> So just to clarify, you want both solutions here?
>
> 1. A gpiochip that covers the entire pin space
> 2. A pinmux implementation that manages pin allocation to the different drivers
>
> In that case we can largely leave this series as is? We only need to
> adjust how we configure the gpiochip by dropping the pin-mapping
> implementation?

Nope. It's far from what I think of. Re-reading again your cover
letter it points out that pin mux per se does not exist in the
hardware. In this case things become a bit too complicated, but we
still may manage to handle them. Before I was thinking about this
hierarchy

1. pinmux driver (which is actually the main driver here)
2. LED driver (using regmap API)
3. GPIO driver (via gpio-regmap)
4. PWM driver.

Now what we need here is some kind of "virtual" pinmux. Do I
understand correctly?

To be clear: I do not like putting everything into one driver when the
logical parts may be separated.

-- 
With Best Regards,
Andy Shevchenko