[U-Boot] usb: dwc2: invalidate the dcache before starting the DMA

[Simon Glass]

Hi Marek,

On 5 April 2017 at 03:35, Marek Vasut <marex at denx.de> wrote:
> On 04/05/2017 04:21 AM, Simon Glass wrote:
>> Hi,
>>
>> On 4 April 2017 at 19:26, Kever Yang <kever.yang at rock-chips.com> wrote:
>>> Hi Eddie,
>>>
>>>
>>>     We should only need to do only one time cache operation for a buffer
>>>
>>> ready to do DMA transfer, so you need to remove another cache invalidate
>>>
>>> operation for the same buffer in the same function.
>>
>> I think this is a more general problem and might cause issues with
>> other drivers. So I have sent this patch:
>>
>> http://patchwork.ozlabs.org/patch/746917/
>>
>
> This feels like papering over a problem though ... which will bite you
> later anyway.

I believe the problem only happens because we have cached zero bytes
caused by this function. If the driver does the right thing (as dwc2.c
already does) then everything should be find from then on.

Notice that the problem does not happen without driver model, since
non-DM code in dwc2.c uses BSS for the buffers, which is zeroed with
the cache off.

Regards,
Simon