Re: [PATCH v4 1/4] dt-bindings: i2c: aspeed: add transfer mode support

[Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>]

Hi Rob,

On 3/6/2021 12:30 PM, Rob Herring wrote:
> 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?

If a given system makes just one byte r/w transactions most of the time
then byte mode will be a right setting. Otherwise, buf mode is more
efficient because it doesn't generate a bunch of interrupts on every
byte handling.

>>   
>>   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.

The example changes are not directly related to the new property but
related to the transfer mode support in this patch set. 'i2c_gr' node is
added to provide a way for accessing I2C global registers to enable
I2C SRAM, and 'reg' is modified to add the SRAM resource range.

Thanks,
Jae

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