linux-kernel - RE: [PATCH v2 1/4] firmware: xilinx: Add sysfs interface

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Date:   Fri, 31 Jan 2020 09:05:15 +0000
From:   Rajan Vaja <RAJANV@...inx.com>
To:     'Greg KH' <gregkh@...uxfoundation.org>,
        Jolly Shah <JOLLYS@...inx.com>
CC:     "ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "matt@...eblueprint.co.uk" <matt@...eblueprint.co.uk>,
        "sudeep.holla@....com" <sudeep.holla@....com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "dmitry.torokhov@...il.com" <dmitry.torokhov@...il.com>,
        Michal Simek <michals@...inx.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 1/4] firmware: xilinx: Add sysfs interface

Hi Greg,

> -----Original Message-----
> From: Greg KH <gregkh@...uxfoundation.org>
> Sent: 31 January 2020 11:41 AM
> To: Jolly Shah <JOLLYS@...inx.com>
> Cc: ard.biesheuvel@...aro.org; mingo@...nel.org; matt@...eblueprint.co.uk;
> sudeep.holla@....com; hkallweit1@...il.com; keescook@...omium.org;
> dmitry.torokhov@...il.com; Michal Simek <michals@...inx.com>; Rajan Vaja
> <RAJANV@...inx.com>; linux-arm-kernel@...ts.infradead.org; linux-
> kernel@...r.kernel.org
> Subject: Re: [PATCH v2 1/4] firmware: xilinx: Add sysfs interface
> 
> EXTERNAL EMAIL
> 
> On Thu, Jan 30, 2020 at 11:59:03PM +0000, Jolly Shah wrote:
> > Hi Greg,
> >
> > On 1/27/20, 10:28 PM, "linux-kernel-owner@...r.kernel.org on behalf of Greg
> KH" <linux-kernel-owner@...r.kernel.org on behalf of
> gregkh@...uxfoundation.org> wrote:
> >
> >     On Mon, Jan 27, 2020 at 11:01:27PM +0000, Jolly Shah wrote:
> >     >     > > > +     ret = kstrtol(tok, 16, &value);
> >     >     > > > +     if (ret) {
> >     >     > > > +             ret = -EFAULT;
> >     >     > > > +             goto err;
> >     >     > > > +     }
> >     >     > > > +
> >     >     > > > +     ret = eemi_ops->ioctl(0, read_ioctl, reg, 0, ret_payload);
> >     >     > >
> >     >     > > This feels "tricky", if you tie this to the device you have your driver
> >     >     > > bound to, will this make it easier instead of having to go through the
> >     >     > > ioctl callback?
> >     >     > >
> >     >     >
> >     >     > GGS(general global storage) registers are in PMU space and linux
> doesn't have access to it
> >     >     > Hence ioctl is used.
> >     >
> >     >     Why not just a "real" call to the driver to make this type of reading?
> >     >     You don't have ioctls within the kernel for other drivers to call,
> >     >     that's not needed at all.
> >     >
> >     > these registers are for users  and for special needs where users wants
> >     > to retain values over resets. but as they belong to PMU address space,
> >     > these interface APIs are provided. They don’t allow access to any
> >     > other registers.
> >
> >     That's not the issue here.  The issue is you are using an "internal"
> >     ioctl, instead just make a "real" call.
> >
> > Sorry I am not clear. Do you mean that we should use linux standard
> > ioctl interface instead of internal ioctl by mentioning "real" ?
> 
> No, you should just make a "real" function call to the exact thing you
> want to do.  Not have an internal multi-plexor ioctl() call that others
> then call.  This isn't a microkernel :)
[Rajan] Sorry for multiple back and forth but as I understand, you are suggesting to create a new API for
Read/write of GGS register instead of using PM_IOCTL API (eemi_ops->ioctl) for multiple purpose. Is my understanding correct?

Thanks,
Rajan

> 
> thanks,
> 
> greg k-h