linux-kernel - Re: [PATCH v2 1/3] mfd: upboard: Add UP2 platform controller driver

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Message-ID: <cdf91d51-dfb5-b2dc-99af-60954cf32255@emutex.com>
Date:   Wed, 31 Oct 2018 20:40:45 +0000
From:   Dan O'Donovan <dan.odonovan@...tex.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Dan O'Donovan <dan.odonovan@...tex.com>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Krogerus, Heikki" <heikki.krogerus@...ux.intel.com>,
        Lee Jones <lee.jones@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        Carlos Iglesias <carlos.iglesias@...tex.com>
Subject: Re: [PATCH v2 1/3] mfd: upboard: Add UP2 platform controller driver


On 10/20/2018 12:49 PM, Andy Shevchenko wrote:
> On Fri, Oct 19, 2018 at 8:26 PM Dan O'Donovan <dan@...tex.com> wrote:
>> From: Javier Arteaga <javier@...tex.com>
>>
>> UP Squared (UP2) is a x86 SBC from AAEON based on Intel Apollo Lake. It
>> features a MAX 10 FPGA that routes lines from both SoC and on-board
>> devices to two I/O headers:
>>
>>                                 +------------------------+
>>                                 | 40-pin RPi-like header |
>>                          +------|         (HAT)          |
>>                          |      +------------------------+
>>     +-------+    +--------+
>>     |       |    |        |     +------------------------+
>>     |  SoC  |----|  FPGA  |-----|  Custom UP2 pin header |
>>     |       |    |        |     |        (EXHAT)         |
>>     +-------+    +--------+     +------------------------+
>>                          |
>>                          +------* On-board devices: LED, VLS...
>>
>> This is intended to enable vendor-specific applications to customize I/O
>> header pinout, as well as include low-latency functionality. It also
>> performs voltage level translation between the SoC (1.8V) and HAT header
>> (3.3V).
>>
>> Out of the box, this block implements a platform controller with a
>> GPIO-bitbanged control interface. It's enumerated by ACPI and provides
>> registers to control:
>>
>> - Configuration of all FPGA-routed header lines. These can be driven
>>   SoC-to-header, header-to-SoC or set in high impedance.
>>
>> - On-board LEDs and enable lines for other platform devices.
>>
>> Add core support for this platform controller as a MFD device, exposing
>> these registers as a regmap.
> Can we see a link to or an excerpt of ACPI table for this device?
Sure: https://gist.github.com/Dan-Emutex/6382c25f4b8b8cdd80e6056889cdf48b
I'll add this to the cover letter for v3 as well.

>
>> +#define set_clear(u, x) gpiod_set_value((u)->clear_gpio, (x))
>> +#define set_strobe(u, x) gpiod_set_value((u)->strobe_gpio, (x))
>> +#define set_datain(u, x) gpiod_set_value((u)->datain_gpio, (x))
>> +#define get_dataout(u) gpiod_get_value((u)->dataout_gpio)
> I think these macros don't bring much value. (Up to you and Lee to decide)
These were added in response to one of your review comments on the original patch-set ;)
I think they do slightly improve the code readability so I'll leave them there if there are no objections.

>
>
>> +static void __reg_io_write(const struct upboard_ddata * const ddata,
>> +                          unsigned int size, unsigned int val)
>> +{
>> +       int i;
>> +
>> +       /*
>> +        * DATAIN is latched on each rising edge of the STROBE signal.
>> +        * Data (register address or value) is sent MSb first.
>> +        */
>> +       for (i = size - 1; i >= 0; i--) {
> while (size--)
Yep, much neater.  I'll change that, thanks!  Ditto for the other comments on this file.+ ret = upboard_init_gpio(dev);

>> +       if (ret) {
>> +               if (ret != -EPROBE_DEFER)
>> +                       dev_err(dev, "failed to init GPIOs: %d", ret);
>> +               return ret;
>> +       }
> I don't know if probe_err() helper is going to be a part of v4.21
> (which this series targets), it would be good to use it.
I left this out for now in case it causes any awkwardness with merging.  Hope that's ok.