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

[Marek Vasut]

On 04/06/2017 04:40 AM, Simon Glass wrote:
> Hi Marek,
> 
> On 5 April 2017 at 19:32, Marek Vasut <marex at denx.de> wrote:
>> On 04/06/2017 03:24 AM, Simon Glass wrote:
>>> Hi Marek,
>>>
>>> On 5 April 2017 at 15:34, Marek Vasut <marex at denx.de> wrote:
>>>> On 04/05/2017 05:03 PM, Simon Glass wrote:
>>>>> +Tom
>>>>>
>>>>> Hi Marek,
>>>>>
>>>>> On 5 April 2017 at 04:21, Marek Vasut <marex at denx.de> wrote:
>>>>>> On 04/05/2017 12:08 PM, Simon Glass wrote:
>>>>>>> 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.
>>>>>>
>>>>>> And I think the driver is where this should be fixed ? That is, the
>>>>>> driver should do the right thing and flush/invalidate caches correctly.
>>>>>>
>>>>>>> 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.
>>>>>
>>>>> I'm not sure if you read the long and windy thread with Stefan B but
>>>>> the upshot is that the driver is doing the right thing.
>>>>>
>>>>> If the driver were doing the memset() then you could make a case that
>>>>> we should change the driver, but since DM is doing it and DM is
>>>>> promising that DMA can be used on the buffer, I think the best place
>>>>> for the fix is in DM. The driver should not need to change and neither
>>>>> should any other driver when we convert it to DM.
>>>>>
>>>>> On that last point I really want to avoid having to change the caching
>>>>> behaviour of drivers just to work with DM!
>>>>
>>>> So will the driver work with your patch and without DM ? I don't think
>>>> so, so I think what Eddie's patch does is correct. I'd really like him
>>>> to send a new version and apply that.
>>>
>>> Yes the driver work fine without DM and the code is correct. The
>>> buffer is in BSS in that case and we don't have the cache problem. I
>>> think we would have seen this problem before :-)
>>
>> I am seeing problems around this code and this patch makes sense to me,
>> so I think this patch should go in as well ...
> 
> OK, well up to you. What sort of problems?

Some sticks are not detected for me and adding a small delay here
magically fixes it. I suspect I'm hitting this cache issue.

-- 
Best regards,
Marek Vasut