Hello Mike and Marek,
On 2/29/2012 3:55 PM, Amit Virdi wrote:
Hello Mike,
On 2/28/2012 6:26 AM, Mike Frysinger wrote:
On Monday 27 February 2012 15:53:29 Marek Vasut wrote:
On Monday 27 February 2012 08:14:26 Marek Vasut wrote:
On 2/25/2012 3:42 PM, Albert ARIBAUD wrote:
Le 24/02/2012 12:58, Amit Virdi a écrit :
Packed attribute is forcing a bytewise write on device registers,
there by, resulting in a misbehavior on gcc-4.4.1.
Reverting the structures to non-packed
If (just asking, not asserting) the issue is caused by fields being
u8 where u8 access is not possible, then should you not make the
fields u16 / u32 according to access requirements?
The problem is not with the fields being of a different width. AFAIK,
the packed attribute changes the generated code to access even the
word field elements in a byte by byte manner
Infact, there is a discussion on lkml that I can point
https://lkml.org/lkml/2011/4/27/278
It seems that the discussion did not lead to a conclusion but it was
sensible (at least for ARM) to remove the packed attribute from this
structure
What does the USB spec say ? It might be a HW bug?
it isn't covered by the USB spec. these are structs for hardware
registers in the EHCI usb host controller.
I see ... so replacing them with unions of accessors where it colides
might
work ?
i'm not entirely sure what you're asking, but i think you're pointing
to the
right answer: drivers/usb/host/ehci.h:ehci_{read,write}l() should
*not* be
casting/derferencing the pointers directly. they should instead be using
standard {read,write}l() funcs from asm/io.h.
Amit: can you post a new patch that does that instead ? don't touch the
packed attribute, but change ehci_readl() to use readl() and
ehci_writel() to
use writel() ?
I'll make the changes and post the patch after testing successfully.
I did the changes suggested by you and tested the build. The issue
didn't come up. Then I reverted the code to the original (attributes
retained and ehci directly de-referencing the pointers. The issue didn't
come here too.
Today, I used armv7-linux-gcc (GCC) v4.6.2
So I suspect there has been some fix done in the GCC.
Now, even with the packed attributes, the word fields are accessed
word-by-word in contrast to the earlier observed behavior
(byte-by-byte). I could see ldr and str in the disassembly.
May be, we can discard this patch and keep drivers/usb/host/ehci.h intact.
Thanks
Amit Virdi
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