Re: [PATCH RFC 4/7] i2c: Add device tree bindings for GENI I2C Controller

From: Rob Herring <robh@kernel.org>
To: Karthik Ramasubramanian <kramasub@codeaurora.org>
Cc: linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	Linux I2C <linux-i2c@vger.kernel.org>,
	linux-serial@vger.kernel.org, linux-doc@vger.kernel.org,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>, Andy Gross <andy.gross@linaro.org>,
	David Brown <david.brown@linaro.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Wolfram Sang <wsa@the-dreams.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	Sagar Dharia <sdharia@codeaurora.org>
Subject: Re: [PATCH RFC 4/7] i2c: Add device tree bindings for GENI I2C Controller
Date: Thu, 11 Jan 2018 09:19:28 -0600	[thread overview]
Message-ID: <CAL_Jsq+2w280okNbUxVqzm2oXWRc81RnMwBaM6utXqg_+fvMkg@mail.gmail.com> (raw)
In-Reply-To: <1d741169-e6e6-1896-d8d4-4f580f5d497d@codeaurora.org>

On Mon, Jan 8, 2018 at 6:33 PM, Karthik Ramasubramanian
<kramasub@codeaurora.org> wrote:
>
>
> On 1/2/2018 8:51 AM, Rob Herring wrote:
>>
>> On Wed, Dec 27, 2017 at 09:27:23AM -0700, Karthikeyan Ramasubramanian
>> wrote:
>>>
>>> Add device tree binding support for I2C Controller in GENI based
>>> QUP Wrapper.
>>>
>>> Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>
>>> Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>
>>> ---
>>>   .../devicetree/bindings/i2c/i2c-qcom-geni.txt      | 39
>>> ++++++++++++++++++++++
>>>   1 file changed, 39 insertions(+)
>>>   create mode 100644
>>> Documentation/devicetree/bindings/i2c/i2c-qcom-geni.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/i2c/i2c-qcom-geni.txt
>>> b/Documentation/devicetree/bindings/i2c/i2c-qcom-geni.txt
>>> new file mode 100644
>>> index 0000000..d2fa9ce
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/i2c/i2c-qcom-geni.txt
>>> @@ -0,0 +1,39 @@
>>> +Qualcomm Technologies Inc. GENI based I2C Controller driver
>>> +
>>> +Required properties:
>>> + - compatible: Should be:
>>> +   * "qcom,i2c-geni.
>>
>>
>> Only 1 version?
>
> The Serial Engine used by I2C protocol has the same version as the QUP h/w
> version. The QUP Wrapper driver exposes an interface function to get the h/w
> version so that I2C controller driver can support version-specific
> operations, if any.
>>
>>
>>> + - reg: Should contain QUP register address and length.
>>> + - interrupts: Should contain I2C interrupt.
>>> + - clocks: Serial engine core clock, and AHB clocks needed by the
>>> device.
>>
>>
>> Are there really clocks for a firmware based device or these are just
>> clocks in the parent serial engine?
>
> The clocks are required to derive the protocol clock. The clocks are also
> required by the Serial Engine to access the System Memory during DMA mode of
> operation.

You can get the QUP core (or Serial engine?) node and then get its
clocks if you need to know the frequency. Put the clocks in DT in the
h/w block they belong to. If you don't really have an I2C clock in the
h/w, don't put one in the DT.

Rob