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

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Message-ID: <20200131061038.GA2180358@kroah.com>
Date:   Fri, 31 Jan 2020 07:10:38 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     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>,
        Rajan Vaja <RAJANV@...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

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 :)

thanks,

greg k-h