linux-kernel - Re: [patch/rfc 2.6.19-rc5] arch-neutral GPIO calls

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <200611131125.52984.david-b@pacbell.net>
Date:	Mon, 13 Nov 2006 11:25:52 -0800
From:	David Brownell <david-b@...bell.net>
To:	"Thiago Galesi" <thiagogalesi@...il.com>
Cc:	"Paul Mundt" <lethal@...ux-sh.org>,
	"Linux Kernel list" <linux-kernel@...r.kernel.org>,
	"Andrew Morton" <akpm@...l.org>,
	"Andrew Victor" <andrew@...people.com>,
	"Bill Gatliff" <bgat@...lgatliff.com>,
	"Haavard Skinnemoen" <hskinnemoen@...el.com>, jamey.hicks@...com,
	"Kevin Hilman" <khilman@...sta.com>,
	"Nicolas Pitre" <nico@....org>,
	"Russell King" <rmk@....linux.org.uk>,
	"Tony Lindgren" <tony@...mide.com>
Subject: Re: [patch/rfc 2.6.19-rc5] arch-neutral GPIO calls

On Monday 13 November 2006 9:56 am, Thiago Galesi wrote:
> I guess that a kind of "name addressing" would be the way to go, we
> need to get to it by "location" (I'm thinking PortA 20, PortB 5 rather
> than pin number or some other arbitrary convention; we need a way to
> not need to look up what 'Port X pin B' should be called.

That's highly platform-specific.  AT91 and AVR32 use that style of
addressing ... most others just talk about GPIO numbers.  In all cases,
the platform can assign _some_ number to each GPIO signal.


> Another thing that may be considered is the ability to get 'pointers'
> for GPIOs.

The GPIO identifiers are unsigned integers.  If you really crave pointers,
you can cast those integers to pointers, and back.  But why bother?  :)


> And, of course, protecting GPIOs from concurrent accesses 

Did you read the proposal?  There are *already* two mechanisms for that:

 - gpio_request()/gpio_free() ... protecting from concurrent access
   between drivers, also known as bugs.

 - gpio_set_value() ... implementations can lock internally, as needed.
   ditto gpio_get_value(), but only bizarre hardware would need it.

Re that last, consider two different types of GPIO controller:

  * One of them has just one register with the output values, and a
    RISC CPU without bit set/clear instructions to use on it.  So a
    spinlock is needed to cover reading the register, modifying that
    value, then rewriting the value.

  * Better GPIO controller designs (normal ones) have separate registers
    for "write mask to set" and "write mask to clear" ... no spinlock
    needed, the hardware sorts everything out.

I did update the docs to make clear that gpio get/set calls are atomic;
hard to imagine single bit operations that aren't, but it's worth
removing potential confusion.

- Dave

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/