linux-kernel - Re: [PATCH v6 08/12] arm64: dts: nuvoton: Add initial ma35d1 device tree

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Date:   Wed, 29 Mar 2023 11:13:11 +0800
From:   Jacky Huang <ychuang570808@...il.com>
To:     Stephen Boyd <sboyd@...nel.org>, gregkh@...uxfoundation.org,
        jirislaby@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        lee@...nel.org, mturquette@...libre.com, p.zabel@...gutronix.de,
        robh+dt@...nel.org
Cc:     devicetree@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        arnd@...db.de, schung@...oton.com, mjchen@...oton.com,
        Jacky Huang <ychuang3@...oton.com>
Subject: Re: [PATCH v6 08/12] arm64: dts: nuvoton: Add initial ma35d1 device
 tree

Dear Stephen,


On 2023/3/29 上午 10:46, Stephen Boyd wrote:
> Quoting Jacky Huang (2023-03-28 19:39:36)
>> On 2023/3/29 上午 10:19, Stephen Boyd wrote:
>>> What do you use the syscon for then? The clock driver must want to use
>>> the syscon for something, implying that they are the same device.
>> The register lock mechanism is applied to protect many critical
>> registers from false written.
>> The register lock control register is one register in system controller.
>> Some registers of the clock controller are lock protected. Not only
>> clock controller, but other
>> IP such as RTC, PWM, ADC, etc, also have lock protected registers. All
>> these IP requires
>> syscon to access the lock/unlock control register in the system controller.
>> That's why we add a <&sys> to the clock controller.
>>
>> Should we implement a ma35d1-sysctl driver to protect register_lock()
>> and register_unlock()
>> and export to those drivers?  If yes, we can remove the <&sys> from
>> clock controller.
>>
> You can implement the lock and unlock in the hwspinlock framework. See
> drivers/hwspinlock.

I may not explain clearly enough. The lock/unlock register of system 
controller is more like
a kind of write protection for specific registers, rather than 
preventing hetero-core CPU access.
In many different IP of ma35d1 contain write protected registers.
In fact, ma35d1 has a "hardware semaphore" IP, and we have implemented 
the driver in drivers/hwspinlock.
Even the control register of "hardware semaphore" is also write protected.

So, should we implement a system controller driver to provide 
register_unlock() function?
Is it OK to have such a driver in drivers/mfd?
Or, just use syscon in device tree for those devices that have write 
protect registers.


Best regards,
Jacky Huang