ARM unaligned MMIO access with attribute((packed))

Rabin Vincent rabin at
Wed Apr 27 10:06:00 EDT 2011

On Wed, Apr 27, 2011 at 00:21, Alan Stern <stern at> 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:
>>       /* force reset to complete */
>>       ehci_writel(ehci, temp & ~(PORT_RWC_BITS | PORT_RESET),
>>                               status_reg);
> Why would that get messed up?  The 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.

More information about the linux-arm-kernel mailing list