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Date:   Fri, 31 Jan 2020 10:36:46 +0100
From:   'Greg KH' <gregkh@linuxfoundation.org>
To:     Rajan Vaja <RAJANV@xilinx.com>
Cc:     Jolly Shah <JOLLYS@xilinx.com>,
        "ard.biesheuvel@linaro.org" <ard.biesheuvel@linaro.org>,
        "mingo@kernel.org" <mingo@kernel.org>,
        "matt@codeblueprint.co.uk" <matt@codeblueprint.co.uk>,
        "sudeep.holla@arm.com" <sudeep.holla@arm.com>,
        "hkallweit1@gmail.com" <hkallweit1@gmail.com>,
        "keescook@chromium.org" <keescook@chromium.org>,
        "dmitry.torokhov@gmail.com" <dmitry.torokhov@gmail.com>,
        Michal Simek <michals@xilinx.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 1/4] firmware: xilinx: Add sysfs interface
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On Fri, Jan 31, 2020 at 09:05:15AM +0000, Rajan Vaja wrote:
> Hi Greg,
> 
> > -----Original Message-----
> > From: Greg KH <gregkh@linuxfoundation.org>
> > Sent: 31 January 2020 11:41 AM
> > To: Jolly Shah <JOLLYS@xilinx.com>
> > Cc: ard.biesheuvel@linaro.org; mingo@kernel.org; matt@codeblueprint.co.uk;
> > sudeep.holla@arm.com; hkallweit1@gmail.com; keescook@chromium.org;
> > dmitry.torokhov@gmail.com; Michal Simek <michals@xilinx.com>; Rajan Vaja
> > <RAJANV@xilinx.com>; linux-arm-kernel@lists.infradead.org; linux-
> > kernel@vger.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@vger.kernel.org on behalf of Greg
> > KH" <linux-kernel-owner@vger.kernel.org on behalf of
> > gregkh@linuxfoundation.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?

That is correct.