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

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Message-ID:
 <SI6PR06MB753542037E1D6BBF5CE8D2E7F2A42@SI6PR06MB7535.apcprd06.prod.outlook.com>
Date: Mon, 24 Mar 2025 08:30:16 +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"
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	<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 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).
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
> 
> 
> Best regards,
> Krzysztof