linux-kernel - Re: [PATCH v7 2/2] drivers/misc: Add Aspeed P2A control driver

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Date:   Wed, 27 Mar 2019 12:01:50 -0700
From:   Patrick Venture <venture@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-aspeed@...ts.ozlabs.org
Subject: Re: [PATCH v7 2/2] drivers/misc: Add Aspeed P2A control driver

On Wed, Mar 27, 2019 at 11:54 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Wed, Mar 27, 2019 at 11:44:36AM -0700, Patrick Venture wrote:
> > On Wed, Mar 27, 2019 at 11:28 AM Greg KH <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Tue, Mar 12, 2019 at 09:31:01AM -0700, Patrick Venture wrote:
> > > > +     phys_addr_t mem_base;
> > >
> > > Is this really a 32bit value?
> >
> > It's going to be a 32-bit value if this is in the dts for one of the
> > correspondingly supported aspeed models.
> >
> > >
> > > Your ioctl thinks it is:
> > >
> > > > +struct aspeed_p2a_ctrl_mapping {
> > > > +     __u32 addr;
> > >
> > > Does this driver not work on a 64bit kernel?
> >
> > This driver is aimed at only 32-bit hardware (ast2400/2500).  I
> > modeled the approach after the aspeed-lpc-ctrl driver as it's
> > providing similar functionality.
> >
> > >
> > > > +     __u32 length;
> > > > +     __u32 flags;
> > > > +};
> > >
> > > addr really should be __u32 here so you don't have to mess with 32/64
> > > bit user/kernel issues, right?
> >
> > Add is __u32 there.  Are you suggesting it shouldn't be?
>
> Ugh, yes, sorry, I meant to say "__u64".
>
> If you all insist that this is all that is ever going to be needed, ok,
> but I reserve the right to complain in 4 years when this needs to be
> changed :)

In the event the ast2600 comes out and is 64-bit -- I can't imagine
that's likely to happen.  I can take solace that this won't be the
only thing that needs retrofitting.  But it wouldn't kill me to just
make the change.  I'll just have to tweak it to return failure in the
event the address provided isn't found in any region...

Is that all that needs to change for 64-bit addressing support - given
your read of the driver?

>
> thanks,
>
> greg k-h