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: <20251028-ingenious-dazzling-jackdaw-af487d@kuoka>
Date: Tue, 28 Oct 2025 08:47:58 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Ryan Chen <ryan_chen@...eedtech.com>, bmc-sw@...eedtech.com, 
	benh@...nel.crashing.org, joel@....id.au, andi.shyti@...nel.org, jk@...econstruct.com.au, 
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, 
	andrew@...econstruct.com.au, p.zabel@...gutronix.de, andriy.shevchenko@...ux.intel.com, 
	naresh.solanki@...ements.com, linux-i2c@...r.kernel.org, openbmc@...ts.ozlabs.org, 
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v21 2/4] dt-bindings: i2c: ast2600-i2c.yaml: Add
 global-regs and transfer-mode properties

On Mon, Oct 27, 2025 at 08:14:45PM +0100, Krzysztof Kozlowski wrote:
> 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?
> 
> >  
> >  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?
> 
> No, fix your example when creating it.

Heh, and this was not even tested... you have warnings here (see
maintainer soc profiles).

Best regards,
Krzysztof