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Date:   Fri, 31 Jan 2020 07:10:38 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Jolly Shah <JOLLYS@xilinx.com>
Cc:     "ard.biesheuvel@linaro.org" <ard.biesheuvel@linaro.org>,
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        Michal Simek <michals@xilinx.com>,
        Rajan Vaja <RAJANV@xilinx.com>,
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        <linux-arm-kernel@lists.infradead.org>,
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Subject: Re: [PATCH v2 1/4] firmware: xilinx: Add sysfs interface
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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 :)

thanks,

greg k-h