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

[Simon Glass]

Hi Marek,

On 6 April 2017 at 04:22, Marek Vasut <marex at denx.de> wrote:
> 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.

Is this with CONFIG_DM_USB or without?

Also does your platform have a write-through or write-back cache?

Regards,
Simon