linux-kernel - RE: [PATCH v1 2/3] gpio: Add support for TPS68470 GPIOs

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Date:   Mon, 12 Jun 2017 09:51:49 +0000
From:   "Mani, Rajmohan" <rajmohan.mani@...el.com>
To:     Sakari Ailus <sakari.ailus@....fi>
CC:     Andy Shevchenko <andy.shevchenko@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        "Alexandre Courbot" <gnurou@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Len Brown" <lenb@...nel.org>
Subject: RE: [PATCH v1 2/3] gpio: Add support for TPS68470 GPIOs

Hi Sakari,

> Subject: Re: [PATCH v1 2/3] gpio: Add support for TPS68470 GPIOs
> 
> Hi Rajmohan and Andy,
> 
> On Sun, Jun 11, 2017 at 03:49:18AM +0000, Mani, Rajmohan wrote:
> > Hi Andy,
> >
> > Thanks for the reviews and patience.
> >
> > >
> > > On Tue, Jun 6, 2017 at 2:55 PM, Rajmohan Mani
> > > <rajmohan.mani@...el.com>
> > > wrote:
> > > > This patch adds support for TPS68470 GPIOs.
> > > > There are 7 GPIOs and a few sensor related GPIOs.
> > > > These GPIOs can be requested and configured as appropriate.
> > >
> > > Besides my below comments, just put it here that I recommended
> > > earlier to provide 2 GPIO chips (one per bank of GPIOs).
> > > It's up to Linus to decide since you didn't follow the recommendation.
> > >
> >
> > Ack.
> > Did you mean to add this in Kconfig or this source file?
> >
> > Here's some more details on these GPIOs.
> > Each of these 7 GPIOs has 2 registers to control the mode, level, drive
> strength, polarity, hysteresis control among other things. Also there are GPDI
> and GPDO registers to control the input and output values of these 7 GPIOs.
> These GPIOs are numbered 0 through 6.
> > The remaining 3 GPIOs are more of special purpose GPIOs that are output
> only, with one register to control all of their output values and drive strengths.
> These GPIOs are named with a special purpose (ENABLE, IDLE and RESET of the
> sensor).
> >
> > > > +#include <linux/gpio.h>
> > > > +#include <linux/gpio/machine.h>
> > >
> > > These shouldn't be in the driver.
> > > Instead use
> > > #include <linux/gpio/driver.h>
> > >
> >
> > Ack
> >
> > > > +#include <linux/mfd/tps68470.h>
> > > > +#include <linux/module.h>
> > > > +#include <linux/platform_device.h>
> > >
> > > > +       if (offset >= TPS68470_N_REGULAR_GPIO) {
> > > > +               offset -= TPS68470_N_REGULAR_GPIO;
> > > > +               reg = TPS68470_REG_SGPO;
> > > > +       }
> > >
> > > Two GPIO chips makes this gone.
> 
> Again, I'm not really worried about this driver, but the ACPI tables. How does
> the difference show there?
> 
> The outputs (s_enable, s_idle and s_resetn) are not numbered in the
> documentation. There grouped, though, but the order in that grouping varies.
> 
> > > > +struct gpiod_lookup_table gpios_table = {
> > > > +       .dev_id = NULL,
> > > > +       .table = {
> > > > +                 GPIO_LOOKUP("tps68470-gpio", 0, "gpio.0",
> GPIO_ACTIVE_HIGH),
> > > > +                 GPIO_LOOKUP("tps68470-gpio", 1, "gpio.1",
> GPIO_ACTIVE_HIGH),
> > > > +                 GPIO_LOOKUP("tps68470-gpio", 2, "gpio.2",
> GPIO_ACTIVE_HIGH),
> > > > +                 GPIO_LOOKUP("tps68470-gpio", 3, "gpio.3",
> GPIO_ACTIVE_HIGH),
> > > > +                 GPIO_LOOKUP("tps68470-gpio", 4, "gpio.4",
> GPIO_ACTIVE_HIGH),
> > > > +                 GPIO_LOOKUP("tps68470-gpio", 5, "gpio.5",
> GPIO_ACTIVE_HIGH),
> > > > +                 GPIO_LOOKUP("tps68470-gpio", 6, "gpio.6",
> GPIO_ACTIVE_HIGH),
> > > > +                 GPIO_LOOKUP("tps68470-gpio", 7, "s_enable",
> > > GPIO_ACTIVE_HIGH),
> > > > +                 GPIO_LOOKUP("tps68470-gpio", 8, "s_idle",
> GPIO_ACTIVE_HIGH),
> > > > +                 GPIO_LOOKUP("tps68470-gpio", 9, "s_resetn",
> > > GPIO_ACTIVE_HIGH),
> > > > +                 {},
> > > > +       },
> > > > +};
> > >
> > > This doesn't belong to the driver.
> > >
> >
> > Ack
> > I have moved this code to the MFD driver
> 
> This information should come from the ACPI tables, it should not be present in
> drivers. Why do you need it?
> 

I have removed the GPIO lookup table code for now.

> > > > +       /*
> > > > +        * Initialize all the GPIOs to 0, just to make sure all
> > > > +        * GPIOs start with known default values. This protects against
> > > > +        * any GPIOs getting set with a value of 1, after TPS68470
> > > > + reset
> > >
> > > So, this is hardware bug. Right? Or misconfiguration of the chip we may
> avoid?
> > >
> >
> > The tps68470 PMIC upon reset, does not have the "power on reset" values.
> > We just initialize the GPIOs with their known default values.
> 
> If that was the case, I bet you could expect interesting behaviour from the
> hardware connected to these pins.
> 
> For what it's worth, the chip documentation states that the reset value for the
> SGPO and GPDO registers is zero, as well as that GPIOs are configured as input
> and the reset value of the s_* outputs is low.
> 
> In other words, I don't think that explicitly setting the values to zero has an
> effect.
>

For now, I have removed this code that sets the GPIOs to zeros. If there are enough findings / reasons, this code may come back.