[U-Boot] [PATCH] dwc: ep0: Allocate and flush dwc->ep0_trb in a cache aligned manner

[Marek Vasut]

On 10/04/2017 03:11 PM, Faiz Abbas wrote:
> Hi,
> 
> On Wednesday 04 October 2017 06:01 PM, Marek Vasut wrote:
>> On 10/04/2017 12:51 PM, Faiz Abbas wrote:
>>> Hi,
>>> On Tuesday 03 October 2017 06:48 PM, Marek Vasut wrote:
>>>> On 10/03/2017 03:17 PM, Faiz Abbas wrote:
>>>>> Hi,
>>>>> On Tuesday 03 October 2017 05:34 PM, Marek Vasut wrote:
>>>>>> On 09/19/2017 01:15 PM, Faiz Abbas wrote:
>>>>>>>  
>>>>>>> -	dwc3_flush_cache((uintptr_t)trb, sizeof(*trb));
>>>>>>> +	dwc3_flush_cache((uintptr_t)dwc->ep0_trb_addr, sizeof(*trb) * 2);
>>>>>>
>>>>>> Why *2 ?
>>>>>
>>>>> Because its allocated as sizeof(*dwc->ep0_trb) * 2 below. This is not
>>>>> strictly required as dwc3_flush_cache() rounds up the size to
>>>>> CACHELINE_SIZE but from a caller POV, flush everything we allocated.
>>>>
>>>> Can the other TRB be in use ? Maybe aligning the TRBs to cacheline size
>>>> would be better ?
>>>>
>>> A single trb is 16 bytes in size and two of them are allocated
>>> contiguously.
>>
>> Why are two allocated continuously ? (I am not dwc3 expert)
> 
> Neither am I. I did try to pad to the dwc_trb structure such that each
> trb is 64 bytes in size but this leads to failures when testing. I
> didn't get a chance to debug this though. I suspect its because the code
> expects the trbs to be contiguous and/or 16 bytes in size.

Maybe that's something you need to check -- why it fails if aligned . Do
the TRBs need to be stored back-to-back ?

> It'll be great if someone can shed light on this.
> 
>>
>>> Originally, a flush on the first trb was flushing both of
>>> them anyway as the minimum flush is CACHELINE_SIZE (64 bytes). This is
>>> not changing any functionality as far as I have tested. Just making sure
>>> cache misaligned warnings don't show up.
>>
>> If you flush 64bytes, you flush more than 2 TRBs, you flush something
>> around those TRBs too.
> 
> Yes and that is why I changed the allocation step to
> ROUND(sizeof(trb) * 2, 64). We use only 32 bytes for two trbs but make
> sure to allocate 64 bytes so that we can safely flush it.
> 
> Thanks
> Faiz
> 


-- 
Best regards,
Marek Vasut