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SubjectRE: [PATCH v2 1/4] firmware: xilinx: Add sysfs interface
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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?

Thanks,
Rajan

>
> thanks,
>
> greg k-h
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