linux-kernel - Re: [PATCH v4 3/5] mfd: Add RTL8231 core device

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Message-ID: <acc18a3b1c02b8f89023451d816031e70bec9320.camel@svanheule.net>
Date:   Thu, 03 Jun 2021 13:28:42 +0200
From:   Sander Vanheule <sander@...nheule.net>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Pavel Machek <pavel@....cz>, Rob Herring <robh+dt@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Michael Walle <michael@...le.cc>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Andrew Lunn <andrew@...n.ch>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/5] mfd: Add RTL8231 core device

On Thu, 2021-06-03 at 13:58 +0300, Andy Shevchenko wrote:
> On Thu, Jun 3, 2021 at 1:01 PM Sander Vanheule <sander@...nheule.net> wrote:
> > 
> > The RTL8231 is implemented as an MDIO device, and provides a regmap
> > interface for register access by the core and child devices.
> > 
> > The chip can also be a device on an SMI bus, an I2C-like bus by Realtek.
> > Since kernel support for SMI is limited, and no real-world SMI
> > implementations have been encountered for this device, this is currently
> > unimplemented. The use of the regmap interface should make any future
> > support relatively straightforward.
> > 
> > After reset, all pins are muxed to GPIO inputs before the pin drivers
> > are enabled. This is done to prevent accidental system resets, when a
> > pin is connected to the parent SoC's reset line.
> > 
> > To provide different read and write semantics for the GPIO data
> > registers, a secondary virtual register range is used to enable separate
> > cacheing properties of pin input and output values.
> 
> caching
> 
> ...
> 
> 
> > +static int rtl8231_reg_read(void *context, unsigned int reg, unsigned int
> > *val)
> > +{
> > +       struct mdio_device *mdio_dev = context;
> > +       int ret;
> > +
> > +       ret = mdiobus_read(mdio_dev->bus, mdio_dev->addr,
> > RTL8231_REAL_REG(reg));
> > +
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       *val = ret & 0xffff;
> > +
> > +       return 0;
> > +}
> > +
> > +static int rtl8231_reg_write(void *context, unsigned int reg, unsigned int
> > val)
> > +{
> > +       struct mdio_device *mdio_dev = context;
> > +
> > +       return mdiobus_write(mdio_dev->bus, mdio_dev->addr,
> > RTL8231_REAL_REG(reg), val);
> > +}
> 
> Hmm... Maybe we can amend regmap-mdio to avoid duplication of the
> above? Something like xlate in gpio-regmap or so?
> 

I wanted to make the masking explicit, but since regmap-mdio currently requires
a register address width of 5 bit, it could move there.

Actually, can we safely assume that any MDIO driver implementing clause-22
access (5-bit register address width) will just ignore higher bits? In that
case, I could just drop these functions and not even modify regmap-mdio. It
appears to work for bitbanged MDIO.


> > +       mdiodev->reset_gpio = devm_gpiod_get_optional(dev, "reset",
> > GPIOD_OUT_LOW);
> 
> Missed
> 
>   if (IS_ERR(mdiodev->reset_gpio))
>     return PTR_ERR(mdiodev->reset_gpio);
> 

Will fix.

Best,
Sander