On Wed, 27 Apr 2011, Arnd Bergmann wrote: > On Wednesday 27 April 2011 18:25:40 Alan Stern wrote: > > On Wed, 27 Apr 2011, Rabin Vincent wrote: > > > > > On Wed, Apr 27, 2011 at 00:21, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Tue, 26 Apr 2011, Rabin Vincent wrote: > > > >> In my case it's this writel() in ehci-hub.c that gets chopped into > > > >> strbs: > > > >> > > > >> ï ï ï /* force reset to complete */ > > > >> ï ï ï ehci_writel(ehci, temp & ~(PORT_RWC_BITS | PORT_RESET), > > > >> ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï status_reg); > > > > > > > > Why would that get messed up? ïThe status_reg variable doesn't have any > > > > __atribute__((packed)) associated with it. > > > > > > The initialization of status_reg is: > > > > > > u32 __iomem *status_reg > > > = &ehci->regs->port_status[(wIndex & 0xff) - 1]; > > > > > > where ehci->regs is a pointer to the packed struct ehci_regs. So, this > > > is the same problem of casting pointers to stricter alignment. > > > > Right. I can understand the compiler complaining about the cast to > > stricter alignment during the initialization. But I don't understand > > why that would affect the code generated for the writel function. > > The compiler does not complain, it just silently assumes that it needs > to do byte accesses. There is no way to tell the compiler to ignore > what it knows about the alignment, other than using inline assembly > for the actual pointer dereference. Most architectures today do that, > but on ARM it comes down to "*(u32 *)status_reg = temp". Ah -- so the compiler associates the alignment attribute with the data value and not with the variable's type? I didn't know that. Alan Stern -- 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
