linux-kernel - Re: [PATCH 0/4] rtc/scmi: Support multiple RTCs

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Message-ID: <20250213082032315c4327@mail.local>
Date: Thu, 13 Feb 2025 09:20:32 +0100
From: Alexandre Belloni <alexandre.belloni@...tlin.com>
To: Peng Fan <peng.fan@....nxp.com>
Cc: Sudeep Holla <sudeep.holla@....com>, Peng Fan <peng.fan@....com>,
	"cristian.marussi@....com" <cristian.marussi@....com>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	"arm-scmi@...r.kernel.org" <arm-scmi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>
Subject: Re: [PATCH 0/4] rtc/scmi: Support multiple RTCs

On 13/02/2025 11:30:33+0800, Peng Fan wrote:
> >> IIUC on any pure DT based system, a device node exists per RTC and hence
> >> platform device associated with it. And the RTC devices are created with
> >> parent pointing to unique platform device.
> >> 
> >> > However i.MX SCMI BBM exports two RTCs(id: 0, id: 1), so to make it work for
> >> > current RTC framework, we could only pick one RTC and pass the id to BBM
> >> > server side.
> >> >
> >> > I am not sure whether Alexandre wanna me to update the code following each
> >> > parent could only support one RTC or else.
> >> >
> >
> >I want you to keep your changes local to your driver. I already stated
> >back in 2018 that you were on your own with the imx-sc driver and that I
> >don't like seeing multiple abstractions for existing RTCs. What is the
> >actual use case behind needing to access both RTCs using Linux?
> >Shouldn't this be handled on your firmware side?
> 
> The firmware exports two RTCs, RTC0 could be handled by Linux, RTC1
> could only be read by Linux and configuable by M7 per current i.MX95 EVK
> firmware.

This doesn't answer the main question, why is this useful? Where is the
time of RTC1 coming from and why would linux set a different time on
RTC0 ? Can't the firwmare just set the same time on both RTC0 and RTC1?
What would someone do if RTC0 and RTC1 don't agree on the time?

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com