[PATCH v6 1/2] dt-bindings: i2c: aspeed: support for AST2600-i2cv2

[Ryan Chen]

Hello Krzysztof,
	

> -----Original Message-----
> From: Krzysztof Kozlowski <krzysztof.kozlowski at linaro.org>
> Sent: Friday, March 3, 2023 4:51 PM
> To: Ryan Chen <ryan_chen at aspeedtech.com>; Wolfram Sang
> <wsa at kernel.org>
> Cc: Joel Stanley <joel at jms.id.au>; Brendan Higgins
> <brendan.higgins at linux.dev>; Krzysztof Kozlowski
> <krzysztof.kozlowski+dt at linaro.org>; Andrew Jeffery <andrew at aj.id.au>;
> devicetree at vger.kernel.org; Philipp Zabel <p.zabel at pengutronix.de>; Rob
> Herring <robh+dt at kernel.org>; Benjamin Herrenschmidt
> <benh at kernel.crashing.org>; linux-aspeed at lists.ozlabs.org;
> linux-arm-kernel at lists.infradead.org; linux-kernel at vger.kernel.org;
> openbmc at lists.ozlabs.org; linux-i2c at vger.kernel.org
> Subject: Re: [PATCH v6 1/2] dt-bindings: i2c: aspeed: support for AST2600-i2cv2
> 
> On 03/03/2023 09:28, Ryan Chen wrote:
> > Hello Krzysztof,
> >
> >> -----Original Message-----
> >> From: Krzysztof Kozlowski <krzysztof.kozlowski at linaro.org>
> >> Sent: Friday, March 3, 2023 4:20 PM
> >> To: Ryan Chen <ryan_chen at aspeedtech.com>; Wolfram Sang
> >> <wsa at kernel.org>
> >> Cc: Joel Stanley <joel at jms.id.au>; Brendan Higgins
> >> <brendan.higgins at linux.dev>; Krzysztof Kozlowski
> >> <krzysztof.kozlowski+dt at linaro.org>; Andrew Jeffery
> >> <andrew at aj.id.au>; devicetree at vger.kernel.org; Philipp Zabel
> >> <p.zabel at pengutronix.de>; Rob Herring <robh+dt at kernel.org>; Benjamin
> >> Herrenschmidt <benh at kernel.crashing.org>;
> >> linux-aspeed at lists.ozlabs.org; linux-arm-kernel at lists.infradead.org;
> >> linux-kernel at vger.kernel.org; openbmc at lists.ozlabs.org;
> >> linux-i2c at vger.kernel.org
> >> Subject: Re: [PATCH v6 1/2] dt-bindings: i2c: aspeed: support for
> >> AST2600-i2cv2
> >>
> >> On 01/03/2023 06:57, Ryan Chen wrote:
> >>> Hello Krzysztof,
> >>>
> >>>> -----Original Message-----
> >>>> From: Krzysztof Kozlowski <krzysztof.kozlowski at linaro.org>
> >>>> Sent: Monday, February 27, 2023 4:25 PM
> >>>> To: Ryan Chen <ryan_chen at aspeedtech.com>; Andrew Jeffery
> >>>> <andrew at aj.id.au>; Brendan Higgins <brendan.higgins at linux.dev>;
> >>>> Benjamin Herrenschmidt <benh at kernel.crashing.org>; Joel Stanley
> >>>> <joel at jms.id.au>; Rob Herring <robh+dt at kernel.org>; Krzysztof
> >>>> Kozlowski <krzysztof.kozlowski+dt at linaro.org>; Philipp Zabel
> >>>> <p.zabel at pengutronix.de>; linux-i2c at vger.kernel.org;
> >>>> openbmc at lists.ozlabs.org; devicetree at vger.kernel.org;
> >>>> linux-arm-kernel at lists.infradead.org;
> >>>> linux-aspeed at lists.ozlabs.org; linux-kernel at vger.kernel.org
> >>>> Subject: Re: [PATCH v6 1/2] dt-bindings: i2c: aspeed: support for
> >>>> AST2600-i2cv2
> >>>>
> >>>> On 26/02/2023 04:13, Ryan Chen wrote:
> >>>>> Add ast2600-i2cv2 compatible and aspeed,global-regs,
> >>>>> aspeed,timeout aspeed,xfer-mode description for ast2600-i2cv2.
> >>>>>
> >>>>> Signed-off-by: Ryan Chen <ryan_chen at aspeedtech.com>
> >>>>> ---
> >>>>>  .../devicetree/bindings/i2c/aspeed,i2c.yaml   | 44
> >> +++++++++++++++++++
> >>>>>  1 file changed, 44 insertions(+)
> >>>>>
> >>>>> diff --git a/Documentation/devicetree/bindings/i2c/aspeed,i2c.yaml
> >>>>> b/Documentation/devicetree/bindings/i2c/aspeed,i2c.yaml
> >>>>> index f597f73ccd87..75de3ce41cf5 100644
> >>>>> --- a/Documentation/devicetree/bindings/i2c/aspeed,i2c.yaml
> >>>>> +++ b/Documentation/devicetree/bindings/i2c/aspeed,i2c.yaml
> >>>>> @@ -49,6 +49,25 @@ properties:
> >>>>>      description:
> >>>>>        states that there is another master active on this bus
> >>>>>
> >>>>> +  aspeed,timeout:
> >>>>> +    type: boolean
> >>>>> +    description: I2C bus timeout enable for master/slave mode
> >>>>
> >>>> Nothing improved here in regards to my last comment.
> >>>
> >>> Yes, as I know your require is about " DT binding to represent
> >>> hardware
> >> setup"
> >>> So I add more description about aspeed,timeout as blow.
> >>>
> >>> ASPEED SOC chip is server product, i2c bus may have fingerprint
> >>> connect to
> >> another board. And also support hotplug.
> >>> The following is board-specific design example.
> >>> Board A                                         Board B
> >>> -------------------------                       ------------------------
> >>> |i2c bus#1(master/slave)  <===fingerprint ===> i2c bus#x (master/slave)|
> >>> |i2c bus#2(master)-> tmp i2c device |          |
> >> |
> >>> |i2c bus#3(master)-> adc i2c device |          |
> >> |
> >>> -------------------------                       ------------------------
> >>>
> >>> aspeed,timout properites:
> >>> For example I2C controller as slave mode, and suddenly disconnected.
> >>> Slave state machine will keep waiting for master clock in for rx/tx
> transmit.
> >>> So it need timeout setting to enable timeout unlock controller state.
> >>> And in another side. In Master side also need avoid suddenly slave
> >> miss(un-plug), Master will timeout and release the SDA/SCL.
> >>>
> >>> Do you mean add those description into ore aspeed,timout properites
> >> description?
> >>
> >> You are describing here one particular feature you want to enable in
> >> the driver which looks non-scalable and more difficult to configure/use.
> >> What I was looking for is to describe the actual configuration you have (e.g.
> >> multi-master) which leads to enable or disable such feature in your
> hardware.
> >> Especially that bool value does not scale later to actual timeout
> >> values in time (ms)...
> >>
> >> I don't know I2C that much, but I wonder - why this should be
> >> specific to Aspeed I2C and no other I2C controllers implement it?
> >> IOW, this looks quite generic and every I2C controller should have
> >> it. Adding it specific to Aspeed suggests that either we miss a
> >> generic property or this should not be in DT at all (because no one else has
> it...).
> >>
> >> Also I wonder, why you wouldn't enable timeout always...
> >>
> >> +Cc Wolfram,
> >> Maybe you know whether bool "timeout" property for one controller
> >> makes sense? Why we do not have it for all controllers?
> >>
> > Because, i2c bus didn’t specific timeout.
> > But SMBus defines a clock low time-out, TIMEOUT of 35 ms.
> >
> > It have definition in SMBus specification.
> > http://smbus.org/specs/SMBus_3_1_20180319.pdf
> > You can check Page 18, Note3 that have timeout description.
> 
> Then you have already property for this - "smbus"?
To be a property "smbus", that would be a big topic, 
I saw fsl i2c also have this.
https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/i2c/i2c-mpc.yaml#L43-L47
So, I just think the "timeout" property.

 
Best regards,
Ryan Chen