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

From: Rajan Vaja <RAJANV@xilinx.com>
To: 'Greg KH' <gregkh@linuxfoundation.org>, Jolly Shah <JOLLYS@xilinx.com>
Cc: "keescook@chromium.org" <keescook@chromium.org>,
	"ard.biesheuvel@linaro.org" <ard.biesheuvel@linaro.org>,
	"matt@codeblueprint.co.uk" <matt@codeblueprint.co.uk>,
	"dmitry.torokhov@gmail.com" <dmitry.torokhov@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Michal Simek <michals@xilinx.com>,
	"sudeep.holla@arm.com" <sudeep.holla@arm.com>,
	"mingo@kernel.org" <mingo@kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"hkallweit1@gmail.com" <hkallweit1@gmail.com>
Subject: RE: [PATCH v2 1/4] firmware: xilinx: Add sysfs interface
Date: Fri, 31 Jan 2020 09:05:15 +0000	[thread overview]
Message-ID: <BYAPR02MB40559D6B62C4532C0EAD0281B7070@BYAPR02MB4055.namprd02.prod.outlook.com> (raw)
In-Reply-To: <20200131061038.GA2180358@kroah.com>

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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