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. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
