linux-kernel - Re: [PATCH 0/2] rtc: pch-rtc: add Intel Series PCH built-in read-only RTC

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Message-ID: <ff8a8a78fefd2639fa0bcc68bbbb98ec9f1f2e4a.camel@yadro.com>
Date:   Mon, 30 Aug 2021 14:56:48 +0300
From:   Ivan Mikhaylov <i.mikhaylov@...ro.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Milton Miller II <miltonm@...ibm.com>
CC:     Paul Fertser <fercerpav@...il.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        <openbmc@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] rtc: pch-rtc: add Intel Series PCH built-in
 read-only RTC

On Tue, 2021-08-17 at 22:05 +0200, Alexandre Belloni wrote:
> On 17/08/2021 18:04:09+0000, Milton Miller II wrote:
> > 
> > On Aug 16, 2021, Alexandre Belloni wrote:
> > > On 15/08/2021 01:42:15+0300, Paul Fertser wrote:
> > > > On Tue, Aug 10, 2021 at 06:44:34PM +0300, Ivan Mikhaylov wrote:
> > > > > Add RTC driver with dt binding tree document. Also this driver
> > > adds one sysfs
> > > > > attribute for host power control which I think is odd for RTC
> > > driver.
> > > > > Need I cut it off and use I2C_SLAVE_FORCE? I2C_SLAVE_FORCE is not
> > > good
> > > > > way too from my point of view. Is there any better approach?
> > > > 
> > > > Reading the C620 datasheet I see this interface also allows other
> > > > commands (wake up, watchdog feeding, reboot etc.) and reading
> > > statuses
> > > > (e.g Intruder Detect, POWER_OK_BAD).
> > > > 
> > > > I think if there's any plan to use anything other but RTC via this
> > > > interface then the driver should be registered as an MFD.
> > > > 
> > > 
> > > This is not the current thinking, if everything is integrated, then
> > > there is no issue registering a watchdog from the RTC driver. I'll
> > > let
> > > you check with Lee...
> > 
> > I think the current statement is "if they are truly disjoint 
> > hardware controls" then an MFD might suffice, but if they require 
> > software cordination the new auxillary bus seems to be desired.
> > 
> 
> Honestly, the auxiliary bus doesn't provide anything that you can't do
> by registering a device in multiple subsystem from a single driver.
> (Lee Jones, Mark Brown and I did complain at the time that this was yet
> another back channel for misuses).
> 
> > > > However, I'm not sure what is the correct interface for
> > > poweroff/reboot
> > > control.
> > 
> > While there is a gpio interface to a simple regulator switch,
> > the project to date has been asserting direct or indirect 
> > gpios etc to control the host.   If these are events to 
> > trigger a change in state and not a direct state change
> > that some controller trys to follow, maybe a message delivery 
> > model?   (this is not to reboot or cycle the bmc).
> > 
> > milton
> 

Alexandre, gentle reminder about this one series. I can get rid off from sysfs
attribute and put it like RO rtc without any additional things for now as
starter.

Thanks.