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

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Date:   Fri, 17 Dec 2021 09:24:43 +0100
From:   gregkh <gregkh@...uxfoundation.org>
To:     Tony Huang 黃懷厚 <tony.huang@...plus.com>
Cc:     Wells Lu 呂芳騰 <wells.lu@...plus.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>,
        Arnd Bergmann <arnd@...db.de>,
        黃懷厚 <tonyhuang.sunplus@...il.com>
Subject: Re: [PATCH v4 2/2] misc: Add iop driver for Sunplus SP7021

On Fri, Dec 17, 2021 at 08:10:45AM +0000, Tony Huang 黃懷厚 wrote:
> Dear Gregkh:
> 
> > > +
> > > +static ssize_t sp_iop_state1_show(struct device *dev, struct
> > > +device_attribute *attr, char *buf) {
> > > +     struct sp_iop *iop = dev_get_drvdata(dev);
> > > +     ssize_t len = 0;
> > > +
> > > +     sp_iop_standby_mode(iop);
> > > +     mdelay(10);
> > > +     sp_iop_s1mode(dev, iop);
> > > +     return len;
> > > +}
> > 
> > This function is not showing anything.
> > 
> 							
> The purpose of this function:							
> SP7021 has three power states:S0, S1 and S3.							
> S0:Default domain is on. IOP domain is on. AO domain is on.							
> S1:Default domain is off. IOP domain is on. AO domain is on.							
> S3:Default domain is off. IOP domain is off. AO domain is on.							
> System enter S1 mode when read sysfs sp_iop_state1,							

That is not what sysfs is for, sorry.

> I hope to provide users with the ability to enter S1 mode by themselves.							
> So I cannot use DEVICE_ATTR. I should use file_operations method.							

No, please use the normal power management callbacks for your driver
that all other drivers use in the kernel.  There is nothing special
about this one driver to warrant a totally new user/kernel api for it.

thanks,

greg k-h