linux-kernel - Re: [PATCH v3 1/3] dt-bindings: pwm: imx: Add optional clock '32k'

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Message-ID: <7b2982e3-7193-459c-8724-c88ab6773058@denx.de>
Date: Thu, 12 Sep 2024 02:15:18 +0200
From: Marek Vasut <marex@...x.de>
To: Frank Li <Frank.li@....com>
Cc: Uwe Kleine-König <ukleinek@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
 Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, Philipp Zabel <p.zabel@...gutronix.de>,
 linux-pwm@...r.kernel.org, devicetree@...r.kernel.org, imx@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 pratikmanvar09@...il.com, francesco@...cini.it,
 Conor Dooley <conor.dooley@...rochip.com>
Subject: Re: [PATCH v3 1/3] dt-bindings: pwm: imx: Add optional clock '32k'

On 9/12/24 12:19 AM, Frank Li wrote:
> On Wed, Sep 11, 2024 at 11:14:15PM +0200, Marek Vasut wrote:
>> On 9/11/24 11:10 PM, Frank Li wrote:
>>> On Wed, Sep 11, 2024 at 10:28:52PM +0200, Marek Vasut wrote:
>>>> On 9/10/24 9:07 PM, Frank Li wrote:
>>>>> The pwm in imx8qxp mipi subsystem require one extra '32k' clock. So
>>>>> increase maxItems for clock and clock-names.
>>>>
>>>> This mentions MIPI subsystem, but the IP in question here is PWM.
>>>
>>> Here, mipi just name of subsystem, not related MIPI IP at all.
>>>
>>> There are many IP in i.MX8QXP mipi subsystem, such as i2c, PWM, MIPI PHY,
>>> MIPI controller, PLL, clock-gate, ...
>>>
>>>>
>>>> Are you sure the clock are assigned to the correct IP ?
>>>>
>>>> Shouldn't the clock be assigned to some MIPI IP instead ?
>>>>
>>>
>>> Are both question still validate if treat 'mipi' just name of subsystem.
>>>
>>>> Could you please clarify this in the commit message ?
>>>
>>> 'mipi' just name of subsystem because the major ip is for MIPI. is word
>>> 'mipi-subsystem' better?
>> Let's find out.
>>
>> What is the 32kHz clock used for in the PWM block ?
> 
> After read document again, it is one option of input, CLKSRC in PWMCR.
Thank you for checking.

It seems PWMCR CLKSRC is currently hard-coded to IPG_HIGH in this PWM 
driver, so the 32kHz clock are currently not used ?

The question is, does it make sense to add them ? And if so, what would 
be the use case compared to current IPG_HIGH ?