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Date:   Fri, 18 Jan 2019 14:24:54 -0700
From:   Nick Crews <ncrews@...gle.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     linux-kernel@...r.kernel.org, groeck@...omium.org,
        sjg@...omium.org, dlaurie@...omium.org,
        Duncan Laurie <dlaurie@...gle.com>, linux-rtc@...r.kernel.org,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Benson Leung <bleung@...omium.org>
Subject: Re: [PATCH v2 5/9] platform/chrome: rtc: Add RTC driver for Wilco EC

Hi Alexandre, thanks for taking the time to review this. I've responded to your
comments inline below. I'll send out a new version of this patch soon.

On Mon, Jan 14, 2019 at 3:26 PM Alexandre Belloni
<alexandre.belloni@...tlin.com> wrote:
>
> Hello,
>
> On 14/01/2019 15:03:52-0700, Nick Crews wrote:
> > diff --git a/drivers/rtc/rtc-wilco-ec.c b/drivers/rtc/rtc-wilco-ec.c
> > new file mode 100644
> > index 000000000000..d8ed791da82d
> > --- /dev/null
> > +++ b/drivers/rtc/rtc-wilco-ec.c
> > @@ -0,0 +1,178 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * RTC interface for Wilco Embedded Controller with R/W abilities
> > + *
> > + * Copyright 2018 Google LLC
> > + *
> > + * The corresponding platform device is typically registered in
> > + * drivers/platform/chrome/wilco_ec/core.c
> > + */
> > +
> > +#include <linux/bcd.h>
> > +#include <linux/err.h>
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/platform_data/wilco-ec.h>
> > +#include <linux/rtc.h>
> > +#include <linux/timekeeping.h>
> > +
> > +#define DRV_NAME "rtc-wilco-ec"
>
> Please get rid of that define.
>

Done.

> > +int wilco_ec_rtc_read(struct device *dev, struct rtc_time *tm)
> > +{
> > +     struct wilco_ec_device *ec = dev_get_drvdata(dev->parent);
> > +     u8 param = EC_CMOS_TOD_READ;
> > +     struct ec_rtc_read rtc;
> > +     struct wilco_ec_message msg = {
> > +             .type = WILCO_EC_MSG_LEGACY,
> > +             .flags = WILCO_EC_FLAG_RAW_RESPONSE,
> > +             .command = EC_COMMAND_CMOS,
> > +             .request_data = &param,
> > +             .request_size = sizeof(param),
> > +             .response_data = &rtc,
> > +             .response_size = sizeof(rtc),
> > +     };
> > +     struct rtc_time calc_tm;
> > +     unsigned long time;
> > +     int ret;
> > +
> > +     ret = wilco_ec_mailbox(ec, &msg);
> > +     if (ret < 0)
> > +             return ret;
> > +
> > +     tm->tm_sec      = rtc.second;
> > +     tm->tm_min      = rtc.minute;
> > +     tm->tm_hour     = rtc.hour;
> > +     tm->tm_mday     = rtc.day;
> > +     /*
> > +      * The RTC stores the month value as 1-12 but the kernel expects 0-11,
> > +      * so ensure invalid/zero month value from RTC is not converted to -1.
>
> I'm pretty sure this is not necessary and will certainly make the core
> think the date is valid when it has obviously been corrupted.

Done, I'll just use rtc.month - 1 always.

>
> > +      */
> > +     tm->tm_mon      = rtc.month ? rtc.month - 1 : 0;
> > +     tm->tm_year     = rtc.year + (rtc.century * 100) - 1900;
> > +     tm->tm_yday     = rtc_year_days(tm->tm_mday, tm->tm_mon, tm->tm_year);
> > +
> > +     /* Compute day of week */
> > +     rtc_tm_to_time(tm, &time);
> > +     rtc_time_to_tm(time, &calc_tm);
> > +     tm->tm_wday = calc_tm.tm_wday;
>
> Do you really need an accurate wday? There are no userspace applications
> that I know of that care and converting back and forth is quite
> expensive.

No, I'm not sure we do need this. Removing it.

>
> > +
> > +     return 0;
> > +}
> > +
> > +int wilco_ec_rtc_write(struct device *dev, struct rtc_time *tm)
> > +{
> > +     struct wilco_ec_device *ec = dev_get_drvdata(dev->parent);
> > +     struct ec_rtc_write rtc;
> > +     struct wilco_ec_message msg = {
> > +             .type = WILCO_EC_MSG_LEGACY,
> > +             .flags = WILCO_EC_FLAG_RAW_RESPONSE,
> > +             .command = EC_COMMAND_CMOS,
> > +             .request_data = &rtc,
> > +             .request_size = sizeof(rtc),
> > +     };
> > +     int year = tm->tm_year + 1900;
> > +     /* Convert from 0=Sunday to 0=Saturday for the EC */
> > +     int wday = tm->tm_wday == 6 ? 0 : tm->tm_wday + 1;
>
> I'm not sure how useful it is to set an accurate wday when the RTC is
> not able to give it back.

This is actually needed. The RTC controls battery charging schedule,
which varies by the day of the week, and it requires this to be set.

>
> > +     int ret;
> > +
> > +     rtc.param       = EC_CMOS_TOD_WRITE;
> > +     rtc.century     = bin2bcd(year / 100);
> > +     rtc.year        = bin2bcd(year % 100);
> > +     rtc.month       = bin2bcd(tm->tm_mon + 1);
> > +     rtc.day         = bin2bcd(tm->tm_mday);
> > +     rtc.hour        = bin2bcd(tm->tm_hour);
> > +     rtc.minute      = bin2bcd(tm->tm_min);
> > +     rtc.second      = bin2bcd(tm->tm_sec);
> > +     rtc.weekday     = bin2bcd(wday);
> > +
> > +     ret = wilco_ec_mailbox(ec, &msg);
> > +     if (ret < 0)
> > +             return ret;
> > +
> > +     return 0;
> > +}
> > +
> > +static const struct rtc_class_ops wilco_ec_rtc_ops = {
> > +     .read_time = wilco_ec_rtc_read,
> > +     .set_time = wilco_ec_rtc_write,
> > +};
> > +
> > +static int wilco_ec_rtc_probe(struct platform_device *pdev)
> > +{
> > +     struct rtc_device *rtc = devm_rtc_device_register(&pdev->dev,
> > +                                                       DRV_NAME,
> > +                                                       &wilco_ec_rtc_ops,
> > +                                                       THIS_MODULE);
>
> Please use devm_rtc_allocate_device() and set rtc->range_min and
> rtc->range_max before registering with rtc_register_device().

Done.

>
> > +     if (IS_ERR(rtc))
> > +             return PTR_ERR(rtc);
> > +
> > +     return 0;
> > +}
> > +
> > +static struct platform_driver wilco_ec_rtc_driver = {
> > +     .driver = {
> > +             .name = DRV_NAME,
> > +     },
> > +     .probe = wilco_ec_rtc_probe,
> > +};
> > +
> > +module_platform_driver(wilco_ec_rtc_driver);
> > +
> > +MODULE_ALIAS("platform:" DRV_NAME);
> > +MODULE_AUTHOR("Nick Crews <ncrews@...gle.com>");
> > +MODULE_LICENSE("GPL v2");
> > +MODULE_DESCRIPTION("Wilco EC RTC driver");
> > --
> > 2.20.1.97.g81188d93c3-goog
> >
>
> --
> Alexandre Belloni, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com

Cheers,
Nick Crews

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