Dear Amit Virdi,
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.
Can you check with different toolchain please?
Best regards, Marek Vasut