Re: usb: gadget: dwc2: RK3308: Transmission to EP OUT stalls at larger packet size

[Minas Harutyunyan <Minas.Harutyunyan@synopsys.com>]

Hi Pavel,

On 2/5/24 19:52, Pavel Hofman wrote:
> 
> 
> Dne 05. 02. 24 v 15:35 Pavel Hofman napsal(a):
>>
>>>
>> It really looks like some DMA performance issue. Stream 980 bytes/ 
>> 250us (bInterval=2) is bitperfect, no dropped packets. While 24 
>> bytes/125us (bInterval=1) gets stuck. IIUC the DMA is not capable of 
>> copying packets every 125us. Please is there any chance to tweak the 
>> performance to handle the 125us packets reliably?
>>
> 
> I tried increasing f_uac2 req_number/UAC2_DEF_REQ_NUM from 2 to 8 and 
> streaming seems to run stable at 125us microframes now (in both 
> directions simultaneously). Please is there any other gadget tweak which 
> could potentially reduce the risk of dropped packets? Something like 
> using plain DMA instead of desc DMA (no idea :-) )...
> 
> Thanks a lot for your expert opinion.


Yes, it's mandatory to increase f_uac2_req_number, at least 4. Obviously 
2 is not enough for descriptor list and main cause of BNA interrupt.
Another suggestion to change DMA mode from DDMA to BDMA as I suggested 
in previous email.

Thanks,
Minas