RE: [PATCH v5 01/11] i2c: Enhance i2c_new_ancillary_device API

From: Biju Das <biju.das.jz@bp.renesas.com>
To: Wolfram Sang <wsa@kernel.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Mark Brown <broonie@kernel.org>
Cc: "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Laurent Pinchart" <laurent.pinchart@ideasonboard.com>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	"Andrzej Hajda" <andrzej.hajda@intel.com>,
	"Neil Armstrong" <neil.armstrong@linaro.org>,
	"Robert Foss" <rfoss@kernel.org>,
	"David Airlie" <airlied@gmail.com>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Kieran Bingham" <kieran.bingham@ideasonboard.com>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Hans Verkuil" <hverkuil-cisco@xs4all.nl>,
	"Alessandro Zummo" <a.zummo@towertech.it>,
	"Alexandre Belloni" <alexandre.belloni@bootlin.com>,
	"Jonas Karlman" <jonas@kwiboo.se>,
	"Jernej Skrabec" <jernej.skrabec@gmail.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Corey Minyard" <cminyard@mvista.com>,
	"Marek Behún" <kabel@kernel.org>,
	"Jiasheng Jiang" <jiasheng@iscas.ac.cn>,
	"Antonio Borneo" <antonio.borneo@foss.st.com>,
	"Abhinav Kumar" <quic_abhinavk@quicinc.com>,
	"Ahmad Fatoum" <a.fatoum@pengutronix.de>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
	"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
	"Fabrizio Castro" <fabrizio.castro.jz@renesas.com>,
	"linux-renesas-soc@vger.kernel.org"
	<linux-renesas-soc@vger.kernel.org>,
	"Mark Brown" <broonie@kernel.org>
Subject: RE: [PATCH v5 01/11] i2c: Enhance i2c_new_ancillary_device API
Date: Tue, 13 Jun 2023 19:31:46 +0000	[thread overview]
Message-ID: <OS0PR01MB59220D794AED55A6B795C3EF8655A@OS0PR01MB5922.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <OS0PR01MB592210CE54A9CF953980DFEE8655A@OS0PR01MB5922.jpnprd01.prod.outlook.com>

Hi Wolfram,

> Subject: RE: [PATCH v5 01/11] i2c: Enhance i2c_new_ancillary_device API
> 
> Hi Wolfram,
> 
> Thanks for the feedback.
> 
> > Subject: RE: [PATCH v5 01/11] i2c: Enhance i2c_new_ancillary_device
> > API
> >
> > Hi Wolfram,
> >
> > Thanks for the feedback.
> >
> > > Subject: Re: [PATCH v5 01/11] i2c: Enhance i2c_new_ancillary_device
> > > API
> > >
> > > Hi everyone,
> > >
> > > > Perhaps we should first think through what an ancillary device
> > > > really is.  My understanding is that it is used to talk to
> > > > secondary addresses of a multi-address I2C slave device.
> > >
> > > As I mentioned somewhere before, this is not the case. Ancillary
> > > devices are when one *driver* handles more than one address.
> > > Everything else has been handled differently in the past (for  all
> > > the
> > uses I am aware of).
> > >
> > > Yet, I have another idea which is so simple that I wonder if it
> > > maybe has already been discussed so far?
> > >
> > > * have two regs in the bindings
> >
> > OK, it is inline with DT maintainers expectation as it is matching
> > with real hw as single device node having two regs.
> >
> > > * use the second reg with i2c_new_client_device to instantiate the
> > >   RTC sibling. 'struct i2c_board_info', which is one parameter, should
> > >   have enough options to pass data, e.g it has a software_node.
> >
> > OK, I can see the below can be passed from PMIC to new client device.
> >
> > 	client->addr = info->addr;
> >
> > 	client->init_irq = info->irq;
> >
> > >
> > > Should work or did I miss something here?
> >
> > I guess it will work. We instantiate appropriate device based On PMIC
> > revision and slave address and IRQ resource passed through 'struct
> > i2c_board_info'
> >
> > Will check this and update you.
> 
> info.irq = irq; -->Irq fine
> info.addr = addr; -->slave address fine
> size = strscpy(info.type, name, sizeof(info.type)); -->instantiation based
> on PMIC version fine.
> 
> 1) How do we share clk details on instantiated device to find is it
> connected to external crystal or external clock source? as we cannot pass
> of_node between PMIC and "i2c_board_info" as it results in pinctrl
> failure. info->platformdata and
> Client->dev.platformdata to retrieve this info??

Or 

I2C instantiation based on actual oscillator bit value, ie, two i2c_device_id's
with one for setting oscillator bit and another for clearing oscillator bit

PMIC driver parses the clock details. Based on firmware version and clock, 
It instantiates either i2c_device_id with setting oscillator bit or
clearing oscillator bit.

Cheers,
Biju