From: "Marek Behún" <kabel@kernel.org>
To: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: linux-rtc@vger.kernel.org, Alessandro Zummo <a.zummo@towertech.it>
Subject: Re: question about firmware RTC design (for rtcwake)
Date: Thu, 8 Jun 2023 11:05:57 +0200 [thread overview]
Message-ID: <20230608110557.16284eb2@thinkpad> (raw)
In-Reply-To: <20230607082828fd8d03fc@mail.local>
On Wed, 7 Jun 2023 10:28:28 +0200
Alexandre Belloni <alexandre.belloni@bootlin.com> wrote:
> On 22/05/2023 23:14:54+0200, Marek Behún wrote:
> > > You probably need to look at rtc-meson-vrtc.c, rtc-fsl-ftm-alarm.c and
> > > rtc-brcmstb-waketimer.c which implement something similar.
> > >
> > > Honestly, I would go for an in-between proposal where you would store
> > > the requested alarm time (or more likely countdown) on
> > > set_alarm/alarm_irq_enable so you would get .read_alarm working.
> > >
> > > However, my main concern is that this is yet another custom protocol. We
> > > can't possibly have a driver for everyone implementing a timer in their
> > > FPGA/CPLD/cortexM.
> > >
> > > How will you communicate with the MCU, can't you use an already existing
> > > driver?
> >
> > The MCU exposes a command interface over I2C. There already are
> > existing commands, which needs to stay for backwards compatibility.
> >
> > It is theoretically possible to simulate an existing RTC device on
> > another I2C address, but I would need to study them, because the boards
> > are shipped with three different MCUs (STM32, GD32, NXP's MKL81) and
> > they sometimes have a little different I2C slave behavior.
> >
> > But I will need to create a platform/mfd driver anyway for the system
> > off handler and GPIO controller. If I am going to create a new driver
> > anyway, why not add the RTC functionality as well?
>
> No, this is not how MFD is working, you will be writing a separate RTC
> driver or reusing an existing one. Have a look at the recent isl1208
THX for the reply.
I have one I2C client through which I need to implement RTC, GPIO and
system power off. I thought such drivers live in drivers/mfd... Am I
wrong?
Marek
> series:
>
> https://lore.kernel.org/linux-rtc/OS0PR01MB5922DAC377266672ADA9FC28864DA@OS0PR01MB5922.jpnprd01.prod.outlook.com/T/#mab0a75187abf7d8aada2c3517ebfdf7241f4bc7a
>
> This patch adds supports for the isl1208 on board of a PMIC, as you can
> see, this is a very small change versus a full blown RTC driver.
next prev parent reply other threads:[~2023-06-08 9:06 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-22 14:46 question about firmware RTC design (for rtcwake) Marek Behún
2023-05-22 19:40 ` Alexandre Belloni
2023-05-22 21:14 ` Marek Behún
2023-06-07 8:28 ` Alexandre Belloni
2023-06-08 9:05 ` Marek Behún [this message]
2023-06-08 9:25 ` Alexandre Belloni
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