linux-kernel - RE: [PATCH v4 2/2] misc: Add iop driver for Sunplus SP7021

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Message-ID: <fdc6efc8c93f45b492930f75f97409e8@sphcmbx02.sunplus.com.tw>
Date:   Fri, 17 Dec 2021 10:24:50 +0000
From:   Tony Huang 黃懷厚 <tony.huang@...plus.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     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>,
        Rob Herring <robh+dt@...nel.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Wells Lu 呂芳騰 <wells.lu@...plus.com>,
        黃懷厚 <tonyhuang.sunplus@...il.com>
Subject: RE: [PATCH v4 2/2] misc: Add iop driver for Sunplus SP7021

Dear Arnd:

> > >>
> > >> 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>
> > >> ---
> > >> Changes in v4:
> > >>  - Addressed comments from Arnd Bergmann.
> >
> > >I don't think you did: I asked you specifically to add code to
> > >interact with the existing in-kernel interfaces to use the
> > >functionality provided by the device. Pick any (at least two)
> > >subsystems and add support, but leave out any custom user space
> > >interfaces (miscdevice, debugfs, sysfs, ...) for the moment.
> >
> >
> >
> > 1. IOP can run sp_iop_platform_driver_shudown() through the poweroff
> > command and the kernel. Perform system power-off actions.
> 
> Do you mean that this method a) cleanly shuts down the iop before the system
> is powered down, or b) the driver_shutdown() callback is used to initiate the
> powerdown of the system itself?
> 
> In case of a) I would not count that as exposing functionality, what you do here
> is just part of any driver. If instead you are trying to use b), this is the wrong
> way of doing it, see drivers/power/reset/ for examples of how to do it right.
> 
> > 2. Wake up the system by relying on the 8051 internal RTC wake-up
> > mechanism and external GPIO input signals to wake up.
> 
> I think those should be exposed with drivers/rtc for the RTC and drivers/gpio/
> for the GPIO driver, and then you can use the device tree to configure which
> GPIO to use as a wakeup and how it's connected to the RTC.
> 

SP7021:
The system is powered off. But 8051 still has power.
The 8051 has a register to control the power-on and power-off of the system.
8051 has RTC register. When the time is up, 8051 powers on the system.
The 8051 can detect GPIO0~7 pins, and GPIO pin high/low can be used as a power-on judgment mechanism for the system.

> > 3.So you ask me to control IOP(8051) through file_operations, not
> > through DEVICE_ATTR
> 
> No, neither of them. Use the appropriate drivers/*/ subsystems for any
> functionality that has an existing subsystem. If there is something that the iop
> does that does not yet have a subsystem, that requires a more thorough design
> discussion for creating a new user interface, ideally in a hardware-independent
> way. You should not start with that until all the normal features (rtc, wakeup,
> suspend, gpio, ...) are supported.
> 
>        Arnd