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Date:   Wed, 7 Jun 2023 10:55:08 +0200
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Subject: Re: [v5 3/5] dt-bindings: mfd: Add aspeed pwm-tach binding
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To:     Billy Tsai <billy_tsai@aspeedtech.com>,
        Patrick Williams <patrick@stwcx.xyz>
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From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <SG2PR06MB33652E18980E9CF8E4F0894D8B53A@SG2PR06MB3365.apcprd06.prod.outlook.com>
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On 07/06/2023 08:26, Billy Tsai wrote:
>         >>
>         >> He felt what he was trying to accomplish met the documented
>         >> expectations.  Are there some changes that need to be done in mfd.txt to
>         >> further clarify when to use it and when not to?
> 
>         > I think mfd.txt clearly states:
>         > "For more complex devices, when the nexus driver has to
>         > probe registers to figure out what child devices exist etc, this should
>         > not be used. In the latter case the child devices will be determined by
>         > the operating system."
> 
> About the mfd:
> For our pwm and tach devices, there is no need to check/apply any hardware register from parent to determine child’s existence or functional.
> They don’t have any dependency on the parent node. In fact, it doesn’t require a specific driver to bind with the "aspeed,ast2600-pwm-tach" label. Their purpose is solely to share the same clock, reset phandle and base address. The main reason for using simple-mfd in this case is because these two independent devices share the same base address.

Actually one more thoughts. I have doubt that you have two independent
devices. If you share the clock, reset line and register address space,
this means *you do not have two independent devices*.

You have most likely only one device.

Best regards,
Krzysztof