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

From: Greg KH <gregkh@linuxfoundation.org>
To: Patrick Venture <venture@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	linux-aspeed@lists.ozlabs.org, Andrew Jeffery <andrew@aj.id.au>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Joel Stanley <joel@jms.id.au>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v7 2/2] drivers/misc: Add Aspeed P2A control driver
Date: Thu, 28 Mar 2019 07:52:31 +0100	[thread overview]
Message-ID: <20190328065231.GB20312@kroah.com> (raw)
In-Reply-To: <CAO=notzwnDtJ9jmEUDsy_tqVKH-+4rO9gd8rpVjKKvQqJsODTQ@mail.gmail.com>

On Wed, Mar 27, 2019 at 12:01:50PM -0700, Patrick Venture wrote:
> On Wed, Mar 27, 2019 at 11:54 AM Greg KH <gregkh@linuxfoundation.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@linuxfoundation.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?

That's all that I noticed at first glance, yes.  I do dislike having
custom user/kernel apis for random chips like this, but I don't know of
a way to have a generic api for them at the moment as I really do not
know what these chips do :(

One would think that the firmware api would work for you, but given the
complexity here, it does not seem that it would match up.

thanks,

greg k-h

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