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Date:   Mon, 14 Jan 2019 17:30:31 -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

Thanks for the comments Alexandre, I've responded to your comments
inline. I'll send out a new version of the patch in a bit

On Mon, Jan 14, 2019 at 3:26 PM -700 Alexandre Belloni 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 in the new patch.

>
> > +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.

OK, I'll get rid of the safety check and just do rtc.month -1.

>
> > +      */
> > +     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.
>

We probably don't, this RTC should only get used for very specific purposes,
and any userspace programs should be using a different RTC.

> > +
> > +     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 on the EC controls battery charging
schedules and thus needs to know the day of the week, and this is the
way to do this.

> > +     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().
>

Thanks, will do this.

> > +     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

Nick Crews
ncrews@...gle.com

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