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

[Simon Glass]

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?

>
>>>
>>> If this also needs to be fixed in DM, so be it.
>>
>> OK.
>>
>> Regards,
>> Simon

Regards,
Simon