linux-kernel - Re: ARM unaligned MMIO access with attribute((packed))

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Message-ID: <BANLkTimxLjvq2GC8_TJJk9OXZ9fPc-JKiA@mail.gmail.com>
Date:	Wed, 27 Apr 2011 19:36:00 +0530
From:	Rabin Vincent <rabin@....in>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org, linux-usb@...r.kernel.org,
	Ulrich Weigand <Ulrich.Weigand@...ibm.com>,
	linux-kernel@...r.kernel.org, gcc@....gnu.org,
	Peter Maydell <peter.maydell@...aro.org>
Subject: Re: ARM unaligned MMIO access with attribute((packed))

On Wed, Apr 27, 2011 at 00:21, Alan Stern <stern@...land.harvard.edu> 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.
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