On Tue, Mar 26, 2013 at 04:15:36PM +0100, Lucas Stach wrote:
> Am Freitag, den 22.03.2013, 14:20 +0100 schrieb Michael Grzeschik:
> > The udc uses an shared dma memory space between hard and software. This
> > memory layout is described in ci13xxx_qh and ci13xxx_td which are marked
> > with the attribute ((packed)).
> >
> > The packed attribute leads the compiler to generate one byte operations
> > for addressing the mapped memory as it believes this memory has no
> > alignement issues as common streaming data. This appeares on armv5
> > machines where the hardware does not support unaligned 32bit operations.
> > Compilers for newer ARMs will probably still generate 32bit operations,
> > as the hardware supports it.
> >
> > The Datasheet of the synopsys core describes, that some operations on
> > the mapped memory need to be atomic double word operations. I.e. the
> > next pointer addressing in the qhead, as otherwise the hardware could
> > read wrong data and totally stuck.
> >
> > This patch fixes that issue by addressing every mapped area operation
> > with explicit readl and writel operations where needed. It also adds an
> > wmb() for the prepared TD data before it gets enqueued into the qhead.
> >
> > We also remove the packed attribute as other patches could not address
> > this memory handling correct and leak new causes for the issue to come
> > back.
> >
> > Signed-off-by: Michael Grzeschik <m.grzeschik@xxxxxxxxxxxxxx>
> > ---
> [...]
> > diff --git a/drivers/usb/chipidea/udc.h b/drivers/usb/chipidea/udc.h
> > index d644574..be60464 100644
> > --- a/drivers/usb/chipidea/udc.h
> > +++ b/drivers/usb/chipidea/udc.h
> > @@ -38,7 +38,7 @@ struct ci13xxx_td {
> > #define TD_CURR_OFFSET (0x0FFFUL << 0)
> > #define TD_FRAME_NUM (0x07FFUL << 0)
> > #define TD_RESERVED_MASK (0x0FFFUL << 0)
> > -} __attribute__ ((packed));
> > +};
> >
> > /* DMA layout of queue heads */
> > struct ci13xxx_qh {
> > @@ -55,7 +55,7 @@ struct ci13xxx_qh {
> > /* 9 */
> > u32 RESERVED;
> > struct usb_ctrlrequest setup;
> > -} __attribute__ ((packed));
> > +};
> >
> Please don't remove the packed attribute, as this is a structure which
> is shared between hardware and software and really needs a fixed layout.
> As all the members of this struct are natural aligned, it should be
> enough to add attribute aligned(4) to tell the compiler that the start
> address of the struct is also 32bit aligned and this way cause it to
> emit 32bit load/stores.
>
> Though, you have to make sure your DMA buffers are really aligned on a
> 32bit boundary or you'll run into the kernels alignment fixup handlers
> or a data abort.
Even better, i will change the attributes like this:
-} __attribute__ ((packed));
+} __attribute__ ((packed, aligned(4)));
and leave the wmb().
Thanks,
Michael
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