Hi Marek,
On Thursday 08 March 2012 03:36 AM, Marek Vasut wrote:
Dear puneets,
Hi Mike,
On Tuesday 06 March 2012 08:37 AM, Mike Frysinger wrote:
* PGP Signed by an unknown key
On Monday 05 March 2012 09:46:21 Puneet Saxena wrote:
As DMA expects the buffers to be equal and larger then
cache lines, This aligns buffers at cacheline.
i don't think this statement is true. DMA doesn't care about alignment
(well, some do, but it's not related to cache lines but rather some
other restriction in the peripheral DMA itself). what does matter is
that cache operations operate on cache lines and not individual bytes.
hence the core arm code was updated to warn when someone told it to
invalidate X bytes but the hardware literally could not, so it had to
invalidate X + Y bytes.
Agreed, Will update the commit message in next patchset.
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
static void flush_invalidate(u32 addr, int size, int flush)
{
+ /*
+ * Size is the bytes actually moved during transaction,
+ * which may not equal to the cache line. This results
+ * stop address passed for invalidating cache may not be aligned.
+ * Therfore making size as multiple of cache line size.
+ */
+ size = ALIGN(size, ARCH_DMA_MINALIGN);
+
if (flush)
flush_dcache_range(addr, addr + size);
else
i think this is wrong and merely hides the errors from higher up instead
of fixing them. the point of the warning was to tell you that the code
was invalidating *too many* bytes. this code still invalidates too many
bytes without any justification as for why it's OK to do here. further,
this code path only matters to the invalidation logic, not the flush
logic. -mike
The sole purpose of this patch to remove the warnings as start/stop
address sent for invalidating
is unaligned. Without this patch code works fine but with lots of
spew...Which we don't want and discussed
in earlier thread which Simon posted. Please have a look on following link.
As I understood, you agree that we need to align start/stop buffer
address and also agree that
to align stop address we need to align size as start address is already
aligned.
Now, "why its OK to do here"?
We could have aligned the size in two places, cache_qtd() and cache_qh()
but then we need to place alignment check
at all the places where size is passed. So I thought better Aligning at
flush_invalidate() and "ALIGN" macro does not
increase the size if size is already aligned.
Actually I have to agree with Mike here. Can you please remove that ALIGN() (and
all others you might have added)? If it does spew, that's ok and it tells us
something is wrong in the USB core subsystem. Such stuff can be fixed in
subsequent patch.
Sorry, I could not understand "(and all others you might have added)".
Do you want me remove any HACK in the patch which is using ALIGN or
making stop address
aligned? The patch has only the above line to make stop address align
and rest of the code makes
start address align. Just to confirm, you are fine with the start
address alignment code in the patch?
Best regards,
Marek Vasut
Thanx & Regards,
Puneet
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