linux-kernel - RE: [PATCH v16 1/3] dt-bindings: i2c: aspeed: support for AST2600-i2cv2

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Message-ID:
 <SI6PR06MB7535BAD19B51A381171A0E64F2A42@SI6PR06MB7535.apcprd06.prod.outlook.com>
Date: Mon, 24 Mar 2025 10:01:36 +0000
From: Ryan Chen <ryan_chen@...eedtech.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
CC: "benh@...nel.crashing.org" <benh@...nel.crashing.org>, "joel@....id.au"
	<joel@....id.au>, "andi.shyti@...nel.org" <andi.shyti@...nel.org>,
	"robh@...nel.org" <robh@...nel.org>, "krzk+dt@...nel.org"
	<krzk+dt@...nel.org>, "conor+dt@...nel.org" <conor+dt@...nel.org>,
	"andrew@...econstruct.com.au" <andrew@...econstruct.com.au>,
	"p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
	"andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-aspeed@...ts.ozlabs.org"
	<linux-aspeed@...ts.ozlabs.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Mo Elbadry <elbadrym@...gle.com>
Subject: RE: [PATCH v16 1/3] dt-bindings: i2c: aspeed: support for
 AST2600-i2cv2

> Subject: Re: [PATCH v16 1/3] dt-bindings: i2c: aspeed: support for
> AST2600-i2cv2
> 
> On 24/03/2025 09:30, Ryan Chen wrote:
> >> Subject: Re: [PATCH v16 1/3] dt-bindings: i2c: aspeed: support for
> >> AST2600-i2cv2
> >>
> >> On 19/03/2025 12:12, Ryan Chen wrote:
> >>>> Subject: Re: [PATCH v16 1/3] dt-bindings: i2c: aspeed: support for
> >>>> AST2600-i2cv2
> >>>>
> >>>> On 17/03/2025 10:21, Ryan Chen wrote:
> >>>>>> Neither this.
> >>>>>>
> >>>>>> So it seems you describe already existing and documented I2C, but
> >>>>>> for some reason you want second compatible. The problem is that
> >>>>>> you do not provide reason from the point of view of bindings.
> >>>>>>
> >>>>>> To summarize: what your users want - don't care. Start properly
> >>>>>> describing hardware and your SoC.
> >>>>>
> >>>>> OK, for ast2600 i2c controller have two register mode setting.
> >>>>> One, I call it is old register setting, that is right now
> >>>>> i2c-aspeed.c .compatible = "aspeed,ast2600-i2c-bus", And there
> >>>>> have a global register
> >>>> that can set i2c controller as new mode register set.
> >>>>> That I am going to drive. That I post is all register in new an
> >>>>> old register
> >> list.
> >>>>>
> >>>>> For example,
> >>>>> Global register [2] = 0 => i2c present as old register set Global
> >>>>> register [2] = 1 => i2c present as new register set
> >>>> It's the same device though, so the same compatible.
> >>>
> >>> Sorry, it is different design, and it share the same register space.
> >>> So that the reason add new compatible "aspeed,ast2600-i2cv2" for
> >>> this
> >> driver.
> >>> It is different register layout.
> >>
> >> Which device is described by the existing "aspeed,ast2600-i2c-bus"
> >> compatible? And which device is described by new compatible?
> >>
> > On the AST2600 SoC, there are up to 16 I2C controller instances (I2C1 ~
> I2C16).
> 
> So you have 16 same devices.
Yes, one driver instance for 16 i2c device. 
> 
> > Each of these controllers is hardwired at the SoC level to use either the
> legacy register layout or the new v2 register layout.
> > The mode is selected by a bit in the global register, these represent two
> different hardware blocks:
> > "aspeed,ast2600-i2c-bus" describes controllers using the legacy register
> layout.
> > "aspeed,ast2600-i2cv2" describes controllers using the new register
> > layout
> 
> Which part of "same device" is not clear? You have one device, one compatible.
> Whatever you do with register layout, is already defined by that compatible. It
> does not matter that you forgot to implement it in the Linux kernel.

Sorry, I still can't catch your point.
I separated the support into two drivers:
i2c-aspeed.c for legacy layout, compatible "aspeed,ast2600-i2c-bus"
i2c-ast2600.c for the new register set, compatible compatible "aspeed,ast2600-i2cv2"
Do you mean I have integrate into 1 driver at i2c-aspeed.c ? can't be separate two driver?
> 
> Best regards,
> Krzysztof