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Date: Sat, 6 Mar 2021 13:30:11 -0700
From: Rob Herring <robh@kernel.org>
To: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
Subject: Re: [PATCH v4 1/4] dt-bindings: i2c: aspeed: add transfer mode support
Message-ID: <20210306203011.GA1152769@robh.at.kernel.org>
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Cc: Mark Rutland <mark.rutland@arm.com>, devicetree@vger.kernel.org,
 linux-aspeed@lists.ozlabs.org, Wolfram Sang <wsa@the-dreams.de>,
 Andrew Jeffery <andrew@aj.id.au>, openbmc@lists.ozlabs.org,
 Brendan Higgins <brendanhiggins@google.com>, linux-i2c@vger.kernel.org,
 Tao Ren <taoren@fb.com>, Cedric Le Goater <clg@kaod.org>
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On Wed, Feb 24, 2021 at 11:17:17AM -0800, Jae Hyun Yoo wrote:
> Append bindings to support transfer mode.
> 
> Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
> Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
> ---
> Changes since v3:
> - None
> 
> Changes since v2:
> - Moved SRAM resources back to default dtsi and added mode selection
>   property.
> 
> Changes since v1:
> - Removed buffer reg settings from default device tree and added the settings
>   into here to show the predefined buffer range per each bus.
> 
>  .../devicetree/bindings/i2c/i2c-aspeed.txt    | 37 +++++++++++++++----
>  1 file changed, 30 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt b/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt
> index b47f6ccb196a..242343177324 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt
> @@ -17,6 +17,20 @@ Optional Properties:
>  - bus-frequency	: frequency of the bus clock in Hz defaults to 100 kHz when not
>  		  specified
>  - multi-master	: states that there is another master active on this bus.
> +- aspeed,i2c-xfer-mode	: should be "byte", "buf" or "dma" to select transfer
> +			  mode defaults to "byte" mode when not specified.
> +
> +			  I2C DMA mode on AST2500 has these restrictions:
> +			    - If one of these controllers is enabled
> +				* UHCI host controller
> +				* MCTP controller
> +			      I2C has to use buffer mode or byte mode instead
> +			      since these controllers run only in DMA mode and
> +			      I2C is sharing the same DMA H/W with them.
> +			    - If one of these controllers uses DMA mode, I2C
> +			      can't use DMA mode
> +				* SD/eMMC
> +				* Port80 snoop

How does one decide between byte or buf mode? 

>  
>  Example:
>  
> @@ -26,20 +40,29 @@ i2c {
>  	#size-cells = <1>;
>  	ranges = <0 0x1e78a000 0x1000>;
>  
> -	i2c_ic: interrupt-controller@0 {
> -		#interrupt-cells = <1>;
> -		compatible = "aspeed,ast2400-i2c-ic";
> +	i2c_gr: i2c-global-regs@0 {
> +		compatible = "aspeed,ast2500-i2c-gr", "syscon";
>  		reg = <0x0 0x40>;
> -		interrupts = <12>;
> -		interrupt-controller;
> +
> +		#address-cells = <1>;
> +		#size-cells = <1>;
> +		ranges = <0x0 0x0 0x40>;
> +
> +		i2c_ic: interrupt-controller@0 {
> +			#interrupt-cells = <1>;
> +			compatible = "aspeed,ast2500-i2c-ic";
> +			reg = <0x0 0x4>;
> +			interrupts = <12>;
> +			interrupt-controller;
> +		};
>  	};
>  
>  	i2c0: i2c-bus@40 {
>  		#address-cells = <1>;
>  		#size-cells = <0>;
>  		#interrupt-cells = <1>;
> -		reg = <0x40 0x40>;
> -		compatible = "aspeed,ast2400-i2c-bus";
> +		reg = <0x40 0x40>, <0x200 0x10>;
> +		compatible = "aspeed,ast2500-i2c-bus";


The example changes are all unrelated to adding the new property. Should 
be a separate patch or just dropped.

>  		clocks = <&syscon ASPEED_CLK_APB>;
>  		resets = <&syscon ASPEED_RESET_I2C>;
>  		bus-frequency = <100000>;
> -- 
> 2.17.1
>