linux-kernel - RE: [PATCH v21 2/4] dt-bindings: i2c: ast2600-i2c.yaml: Add global-regs and transfer-mode properties

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Message-ID:
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Date: Wed, 29 Oct 2025 09:25:09 +0000
From: Ryan Chen <ryan_chen@...eedtech.com>
To: Krzysztof Kozlowski <krzk@...nel.org>, BMC-SW <BMC-SW@...eedtech.com>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>, "joel@....id.au"
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	<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>, "naresh.solanki@...ements.com"
	<naresh.solanki@...ements.com>, "linux-i2c@...r.kernel.org"
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	<devicetree@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-aspeed@...ts.ozlabs.org"
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	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v21 2/4] dt-bindings: i2c: ast2600-i2c.yaml: Add
 global-regs and transfer-mode properties

> Subject: Re: [PATCH v21 2/4] dt-bindings: i2c: ast2600-i2c.yaml: Add global-regs
> and transfer-mode properties
> 
> On 27/10/2025 07:12, Ryan Chen wrote:
> > The AST2600 I2C controller supports three transfer modes: byte,
> > buffer, and DMA. To allow board designers and firmware to explicitly
> > select the preferred transfer mode for each controller instance.
> > "aspeed,transfer-mode" to allow device tree to specify the desired
> > transfer method used by each I2C controller instance.
> >
> > And AST2600 i2c controller have two register mode, one is legacy
> > register layout which is mix controller/target register control
> > together, another is new mode which is separate controller/target
> > register control.
> >
> 
> This implies your "reg" properties have now completely different meaning and
> this would be quite an ABI break. We discussed this probably 15 revisions ago.
> Where did you document the resolution of that discussion?

Let me explain more about "reg"
The 'reg' property continues to describe the same register regions
(bus and buffer) as in the legacy layout. The selection between the legacy
and new register layout is controlled by a bit in the SoC-level global
register block, referenced through the new 'aspeed,global-regs' property.
Therefore, the meaning of the 'reg' property does not change and no DT ABI
break occurs.

Should I add it in commit message about "reg" ?

> 
> >
> >  unevaluatedProperties: false
> >
> > @@ -57,10 +85,12 @@ examples:
> >        #address-cells = <1>;
> >        #size-cells = <0>;
> >        compatible = "aspeed,ast2600-i2c-bus";
> > -      reg = <0x40 0x40>;
> > +      reg = <0x80 0x80>, <0xc00 0x20>;
> 
> Not relevant to this patch. You just added this line in patch #1, so did you add
> incorrect code just to fix it right away?

I will fix it in patch #1.
> 
> No, fix your example when creating it.
> 
> 
> Best regards,
> Krzysztof