From: Russell King - ARM Linux <linux@arm.linux.org.uk> To: Arnd Bergmann <arnd@arndb.de> Cc: Alan Stern <stern@rowland.harvard.edu>, gregkh@suse.de, Nicolas Pitre <nico@fluxnic.net>, linux-usb@vger.kernel.org, lkml <linux-kernel@vger.kernel.org>, Rabin Vincent <rabin@rab.in>, Alexander Holler <holler@ahsoftware.de>, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] USB: ehci: use packed, aligned(4) instead of removing the packed attribute Date: Mon, 20 Jun 2011 20:02:40 +0100 [thread overview] Message-ID: <20110620190240.GJ26089@n2100.arm.linux.org.uk> (raw) In-Reply-To: <201106201858.45624.arnd@arndb.de> On Mon, Jun 20, 2011 at 06:58:45PM +0200, Arnd Bergmann wrote: > A recent change in gcc changed the default behaviour when compiling the > ehci driver on ARM, but the behaviour was already nondeterministic > because the definition of the readl/writel macros on ARM relies on > unspecified behaviour (cast to pointer with larger aligment). It's unspecified behaviour period. If you pass a pointer to readl/writel which is not word aligned, what you get back is anyones guess. Unaligned load/stores to devices are 'unpredictable' on ARM, and are probably unpredictable on any other sane arch (unless you can predict how the load is going to be issued on the bus, how the peripheral is going to respond, and how the bus activity is going to be assembled into a word.) So, to issue a readl against an u16 pointer is unpredictable not only due to the C language, but also from the sanity point of view. > We are also going to change the ARM implementation to always do 32 bit > accesses in readl/writel, but the patch that went into the ehci driver > was correct nonetheless. Not without someone doing a comparitively large amount of work to analyze the effect of any change there and make sure that it doesn't have a negative impact to drivers.
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From: linux@arm.linux.org.uk (Russell King - ARM Linux) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH] USB: ehci: use packed, aligned(4) instead of removing the packed attribute Date: Mon, 20 Jun 2011 20:02:40 +0100 [thread overview] Message-ID: <20110620190240.GJ26089@n2100.arm.linux.org.uk> (raw) In-Reply-To: <201106201858.45624.arnd@arndb.de> On Mon, Jun 20, 2011 at 06:58:45PM +0200, Arnd Bergmann wrote: > A recent change in gcc changed the default behaviour when compiling the > ehci driver on ARM, but the behaviour was already nondeterministic > because the definition of the readl/writel macros on ARM relies on > unspecified behaviour (cast to pointer with larger aligment). It's unspecified behaviour period. If you pass a pointer to readl/writel which is not word aligned, what you get back is anyones guess. Unaligned load/stores to devices are 'unpredictable' on ARM, and are probably unpredictable on any other sane arch (unless you can predict how the load is going to be issued on the bus, how the peripheral is going to respond, and how the bus activity is going to be assembled into a word.) So, to issue a readl against an u16 pointer is unpredictable not only due to the C language, but also from the sanity point of view. > We are also going to change the ARM implementation to always do 32 bit > accesses in readl/writel, but the patch that went into the ehci driver > was correct nonetheless. Not without someone doing a comparitively large amount of work to analyze the effect of any change there and make sure that it doesn't have a negative impact to drivers.
next prev parent reply other threads:[~2011-06-20 19:02 UTC|newest] Thread overview: 124+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-04-27 14:34 [PATCH] echi: remove structure packing from ehci_def Rabin Vincent 2011-04-27 14:34 ` Rabin Vincent 2011-04-27 15:15 ` Sergei Shtylyov 2011-04-27 15:15 ` Sergei Shtylyov 2011-04-27 15:37 ` [PATCHv2] " Rabin Vincent 2011-04-27 15:37 ` Rabin Vincent 2011-06-16 16:17 ` [PATCH] USB: ehci: use packed,aligned(4) instead of removing the packed attribute Alexander Holler 2011-06-16 16:17 ` [PATCH] USB: ehci: use packed, aligned(4) " Alexander Holler 2011-06-16 17:09 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern 2011-06-16 17:09 ` Alan Stern 2011-06-16 17:55 ` Arnd Bergmann 2011-06-16 17:55 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann 2011-06-16 19:25 ` [PATCH] USB: ehci: use packed,aligned(4) " Alexander Holler 2011-06-16 19:25 ` Alexander Holler 2011-06-16 19:46 ` Alan Stern 2011-06-16 19:46 ` Alan Stern 2011-06-16 20:10 ` Alexander Holler 2011-06-16 20:10 ` Alexander Holler 2011-06-16 20:20 ` Arnd Bergmann 2011-06-16 20:20 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann 2011-06-19 15:02 ` [PATCH] USB: ehci: use packed,aligned(4) " Nicolas Pitre 2011-06-19 15:02 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-19 19:00 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern 2011-06-19 19:00 ` Alan Stern 2011-06-19 20:02 ` Arnd Bergmann 2011-06-19 20:02 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann 2011-06-19 20:11 ` [PATCH] USB: ehci: use packed,aligned(4) " Arnd Bergmann 2011-06-19 20:11 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann 2011-06-19 21:39 ` [PATCH] USB: ehci: use packed,aligned(4) " Nicolas Pitre 2011-06-19 21:39 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-19 21:27 ` [PATCH] USB: ehci: use packed,aligned(4) " Nicolas Pitre 2011-06-19 21:27 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-20 15:03 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern 2011-06-20 15:03 ` Alan Stern 2011-06-20 16:16 ` Nicolas Pitre 2011-06-20 16:16 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-20 16:48 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern 2011-06-20 16:48 ` Alan Stern 2011-06-20 16:58 ` Arnd Bergmann 2011-06-20 16:58 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann 2011-06-20 19:02 ` Russell King - ARM Linux [this message] 2011-06-20 19:02 ` Russell King - ARM Linux 2011-06-20 19:20 ` Nicolas Pitre 2011-06-20 19:20 ` Nicolas Pitre 2011-06-20 19:29 ` Nicolas Pitre 2011-06-20 19:29 ` Nicolas Pitre 2011-06-20 17:10 ` [PATCH] USB: ehci: use packed,aligned(4) " Nicolas Pitre 2011-06-20 17:10 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-20 17:35 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern 2011-06-20 17:35 ` Alan Stern 2011-06-20 18:48 ` Russell King - ARM Linux 2011-06-20 18:48 ` Russell King - ARM Linux 2011-06-20 20:26 ` Arnd Bergmann 2011-06-20 20:26 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann 2011-06-20 20:50 ` Nicolas Pitre 2011-06-20 20:50 ` Nicolas Pitre 2011-06-20 20:55 ` [PATCH] USB: ehci: use packed,aligned(4) " Russell King - ARM Linux 2011-06-20 20:55 ` Russell King - ARM Linux 2011-06-20 21:23 ` Arnd Bergmann 2011-06-20 21:23 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann 2011-06-20 22:23 ` [PATCH] USB: ehci: use packed,aligned(4) " Nicolas Pitre 2011-06-20 22:23 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-21 11:25 ` [PATCH] USB: ehci: use packed,aligned(4) " Arnd Bergmann 2011-06-21 11:25 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann 2011-06-25 1:25 ` Nicolas Pitre 2011-06-25 8:09 ` Arnd Bergmann 2011-06-28 18:51 ` Nicolas Pitre 2011-06-29 10:56 ` Arnd Bergmann 2011-06-20 19:14 ` [PATCH] USB: ehci: use packed,aligned(4) " Nicolas Pitre 2011-06-20 19:14 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-20 19:32 ` Russell King - ARM Linux 2011-06-20 19:32 ` Russell King - ARM Linux 2011-06-20 20:14 ` Arnd Bergmann 2011-06-20 20:14 ` Arnd Bergmann 2011-06-20 20:42 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern 2011-06-20 20:42 ` Alan Stern 2011-06-20 22:36 ` Nicolas Pitre 2011-06-20 22:36 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-21 15:06 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern 2011-06-21 15:06 ` Alan Stern 2011-06-20 17:39 ` Alexander Holler 2011-06-20 17:39 ` Alexander Holler 2011-06-20 18:39 ` Alan Stern 2011-06-20 18:39 ` Alan Stern 2011-06-20 18:46 ` Alexander Holler 2011-06-20 18:46 ` Alexander Holler 2011-06-20 18:57 ` Alan Stern 2011-06-20 18:57 ` Alan Stern 2011-06-20 19:56 ` Nicolas Pitre 2011-06-20 19:56 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-20 21:04 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern 2011-06-20 21:04 ` Alan Stern 2011-06-20 22:31 ` Nicolas Pitre 2011-06-20 22:31 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-21 14:58 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern 2011-06-21 14:58 ` Alan Stern 2011-06-21 20:41 ` Nicolas Pitre 2011-06-21 20:41 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-22 6:23 ` [PATCH] USB: ehci: use packed,aligned(4) " Alexander Holler 2011-06-22 6:23 ` Alexander Holler 2011-06-20 20:09 ` Arnd Bergmann 2011-06-20 20:09 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann 2011-06-20 21:05 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern 2011-06-20 21:05 ` Alan Stern 2011-06-20 20:07 ` Arnd Bergmann 2011-06-20 20:07 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann 2011-06-20 20:28 ` [PATCH] USB: ehci: use packed,aligned(4) " Nicolas Pitre 2011-06-20 20:28 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre 2011-06-20 20:39 ` Arnd Bergmann 2011-06-20 20:39 ` Arnd Bergmann 2011-06-20 21:03 ` Nicolas Pitre 2011-06-20 21:03 ` Nicolas Pitre 2011-06-23 9:47 ` Alexander Holler 2011-06-23 9:47 ` Alexander Holler 2011-06-23 14:25 ` Alan Stern 2011-06-23 14:25 ` Alan Stern 2011-06-24 11:40 ` Alexander Holler 2011-06-24 11:40 ` Alexander Holler 2011-06-20 16:26 ` [PATCH] USB: ehci: use packed,aligned(4) " Arnd Bergmann 2011-06-20 16:26 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann 2011-06-16 20:30 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern 2011-06-16 20:30 ` Alan Stern 2011-06-16 18:16 ` Alexander Holler 2011-06-16 18:16 ` Alexander Holler
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