[U-Boot] [PATCH v8] usb: align buffers at cacheline

puneets puneets at nvidia.com
Wed Mar 7 10:20:55 CET 2012

Hi Mike,
Forgot to write the link in below mail.
Here is the link: 
Do you want me to show a warning where I am making size as cacheline size?

Thanx & Regards,,
On Wednesday 07 March 2012 12:42 PM, puneets wrote:
> 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.
>> * Unknown Key
>> * 0xE837F581
> Thanx&  Regards,
> Puneet

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