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Message-ID: <d1e067a7-81ed-4962-bc38-9db1697514da@linaro.org>
Date: Thu, 16 Nov 2023 12:37:48 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Chris Packham <Chris.Packham@...iedtelesis.co.nz>,
"wsa@...nel.org" <wsa@...nel.org>,
"andi.shyti@...nel.org" <andi.shyti@...nel.org>,
"robh+dt@...nel.org" <robh+dt@...nel.org>,
"krzysztof.kozlowski+dt@...aro.org"
<krzysztof.kozlowski+dt@...aro.org>,
"conor+dt@...nel.org" <conor+dt@...nel.org>,
"gregory.clement@...tlin.com" <gregory.clement@...tlin.com>
Cc: "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 1/2] dt-bindings: i2c: add bus-reset-gpios property
On 15/11/2023 22:53, Chris Packham wrote:
> Hi Krystof,
>
> On 16/11/23 10:29, Krzysztof Kozlowski wrote:
>> On 15/11/2023 04:57, Chris Packham wrote:
>>> Add bus-reset-gpios and bus-reset-duration-us properties to the binding
>>> description for i2c busses. These can be used to describe hardware where
>>> a common reset GPIO is connected to all downstream devices on and I2C
>>> bus. This reset will be asserted then released before the downstream
>>> devices on the bus are probed.
>>>
>>> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
>>> ---
>>>
>> ...
>>
>>> Documentation/devicetree/bindings/i2c/i2c.txt | 8 ++++++++
>>> 1 file changed, 8 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
>>> index fc3dd7ec0445..3f95d71b9985 100644
>>> --- a/Documentation/devicetree/bindings/i2c/i2c.txt
>>> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt
>>> @@ -99,6 +99,14 @@ wants to support one of the below features, it should adapt these bindings.
>>> indicates that the system is accessible via this bus as an endpoint for
>>> MCTP over I2C transport.
>>>
>>> +- bus-reset-gpios:
>>> + GPIO pin providing a common reset for all downstream devices. This GPIO
>>> + will be asserted then released before the downstream devices are probed.
>> I initially reviewed it, but did not think enough about it. After more
>> consideration, I believe this is not a property of the I2C bus
>> controller. This is a property of each device, even if the GPIO is the same.
>>
>> Linux kernel already supports shared GPIO, so you only need
>> enable-ref-counting on it.
>
> That's the kind of breadcrumb I need. Although I can't see
> enable-ref-counting as any kind of DT property. Do you mean
> GPIOD_FLAGS_BIT_NONEXCLUSIVE?
It's not a feature or property of Devicetree, but missing feature of OS.
Best regards,
Krzysztof
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