linux-kernel - Re: [PATCH v3 2/2] misc: Add iop driver for Sunplus SP7021

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Date:   Fri, 17 Dec 2021 17:09:13 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Tony Huang 黃懷厚 <tony.huang@...plus.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Tony Huang <tonyhuang.sunplus@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Derek Kiernan <derek.kiernan@...inx.com>,
        Dragan Cvetic <dragan.cvetic@...inx.com>,
        gregkh <gregkh@...uxfoundation.org>,
        Wells Lu 呂芳騰 <wells.lu@...plus.com>
Subject: Re: [PATCH v3 2/2] misc: Add iop driver for Sunplus SP7021

On Fri, Dec 17, 2021 at 4:16 PM Tony Huang 黃懷厚 <tony.huang@...plus.com> wrote:
> > On Thu, Dec 9, 2021 at 9:58 AM Tony Huang <tonyhuang.sunplus@...il.com>
> > wrote:
> > >
> > > IOP (IO Processor) embedded inside SP7021 which is used as Processor
> > > for I/O control, RTC wake-up and cooperation with CPU & PMC in power
> > > management purpose.
> > > The IOP core is DQ8051, so also named IOP8051, it supports dedicated
> > > JTAG debug pins which share with SP7021.
> > > In standby mode operation, the power spec reach 400uA.
> > >
> > > Signed-off-by: Tony Huang <tonyhuang.sunplus@...il.com>
> >
> > Thanks for the improvements, this again looks better than the previous version.
> > I still have some minor comments, and there are a couple of details I have
> > commented on before that would need to be addressed, but let's focus on the
> > one main issue for now:
> >
> > The driver still doesn't actually /do/ anything: you load the firmware when the
> > driver is loaded, and you shut it down when the driver is removed, but
> > otherwise there is no way to interact with the iop. You had the miscdevice
> > earlier, and you still register that, but there are no file_operations associated
> > with it, so it still doesn't have any effect.
> >
> > In the original version you had a couple of user-side interfaces, for which Greg
> > and I commented that they were not using the correct abstractions, and you
> > still list them in the changelog text as "I/O control, RTC wake-up and
> > cooperation with CPU & PMC in power management".
> >
> > If you want to make any progress with adding the driver, I'd say you should
> > implement at least two of those high-level interfaces that interact with the
> > respective kernel subsystems in order to show that the abstraction works.
> >
>
> Q:"with respective kernel subsystems in order to show that the abstraction works."
> May I ask you about repective kernel subsystem.
> If I use the file_operation method
> Provide user can read and write IOP(8051)'s register.
> Is this a repective kernel subsystem?
> if not
> There are other driver code can give me reference

- For gpio, there are lots of drivers in drivers/gpio/
- For RTC, there are drivers in drivers/rtc/
- For suspending the CPU core, there are drivers in drivers/cpuidle/
- For turning off the system, you can find drivers in drivers/power/reset/

Any of these drivers can interface with your kernel driver in various ways
that avoid adding a custom miscdevice.

         Arnd