From: Ivan Mikhaylov <fr0st61te@gmail.com>
To: fercerpav@gmail.com
Cc: i.mikhaylov@yadro.com, a.zummo@towertech.it,
alexandre.belloni@bootlin.com, linux-kernel@vger.kernel.org,
openbmc@lists.ozlabs.org
Subject: Re: [PATCH 1/2] rtc: pch-rtc: add RTC driver for Intel Series PCH
Date: Fri, 20 Aug 2021 15:34:10 +0300 [thread overview]
Message-ID: <20210820123410.46539-1-fr0st61te@gmail.com> (raw)
In-Reply-To: <20210814225242.GY15173@home.paul.comp>
On Tue, Aug 15, 2021 at 01:52:42PM +0300, Paul Fertser wrote:
> On Tue, Aug 10, 2021 at 06:44:35PM +0300, Ivan Mikhaylov wrote:
> > +config RTC_DRV_PCH
> > + tristate "PCH RTC driver"
> > + help
> > + If you say yes here you get support for the Intel Series PCH
>
> I'm afraid this is really lacking some specification of devices that
> are supported. Is it really everything that Intel currently calls PCH?
Yes, from infromation that I know.
> > +static int pch_rtc_read_time(struct device *dev, struct rtc_time *tm)
> > +{
> > + struct i2c_client *client = to_i2c_client(dev);
> > + struct pch *pch = i2c_get_clientdata(client);
> > + unsigned char rtc_data[NUM_TIME_REGS] = {0};
> > + int rc;
> > +
> > + rc = regmap_bulk_read(pch->regmap, PCH_REG_SC, rtc_data, NUM_TIME_REGS);
> > + if (rc < 0) {
> > + dev_err(dev, "fail to read time reg(%d)\n", rc);
> > + return rc;
> > + }
>
> Citing 26.7.2.3 from C620 (Lewisburg/Purley) datasheet:
>
> "The PCH SMBus slave interface only supports Byte Read operation. The
> external SMBus master will read the RTC time bytes one after
> another. It is software’s responsibility to check and manage the
> possible time rollover when subsequent time bytes are read.
>
> For example, assuming the RTC time is 11 hours: 59 minutes: 59
> seconds. When the external SMBus master reads the hour as 11, then
> proceeds to read the minute, it is possible that the rollover happens
> between the reads and the minute is read as 0. This results in 11
> hours: 0 minutes instead of the correct time of 12 hours: 0 minutes.
> Unless it is certain that rollover will not occur, software is
> required to detect the possible time rollover by reading multiple
> times such that the read time bytes can be adjusted accordingly if
> needed."
>
> Should this be taken additional care of somehow?
1. .use_single_read in regmap_config.
2. Maybe that is the right place for rollover check.
> > +static ssize_t force_off_store(struct device *dev,
> > + struct device_attribute *attr,
> > + const char *buf, size_t count)
> > +{
> > + struct i2c_client *client = to_i2c_client(dev);
> > + struct pch *pch = i2c_get_clientdata(client);
> > + unsigned long val;
> > + int rc;
> > +
> > + if (kstrtoul(buf, 10, &val))
> > + return -EINVAL;
> > +
> > + if (val) {
> > + /* 0x02 host force off */
>
> I wonder why you write "host force off" while the C620 datasheet calls
> it "Unconditional Power Down", does your PCH manual use different
> naming?
It just a synonym, does the same. I can change it but first it's need to
be decided if attribute would go or not.
Thanks.
next prev parent reply other threads:[~2021-08-23 0:26 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-10 15:44 [PATCH 0/2] rtc: pch-rtc: add Intel Series PCH built-in read-only RTC Ivan Mikhaylov
2021-08-10 15:44 ` [PATCH 1/2] rtc: pch-rtc: add RTC driver for Intel Series PCH Ivan Mikhaylov
2021-08-14 22:52 ` Paul Fertser
2021-08-20 12:34 ` Ivan Mikhaylov [this message]
2021-09-25 22:24 ` Alexandre Belloni
2021-08-10 15:44 ` [PATCH 2/2] dt-bindings: rtc: provide RTC PCH device tree binding doc Ivan Mikhaylov
2021-08-14 22:42 ` [PATCH 0/2] rtc: pch-rtc: add Intel Series PCH built-in read-only RTC Paul Fertser
2021-08-14 23:22 ` Alexandre Belloni
2021-08-17 18:04 ` Milton Miller II
2021-08-17 20:05 ` Alexandre Belloni
2021-08-30 11:56 ` Ivan Mikhaylov
2021-09-14 23:52 ` Ivan Mikhaylov
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