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

[Marek Vasut]

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 ...

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


-- 
Best regards,
Marek Vasut