Re: [PATCH] usb: dwc3: gadget: Init only available HW eps

From: Felipe Balbi <balbi@kernel.org>
To: Thinh Nguyen <Thinh.Nguyen@synopsys.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	Bryan O'Donoghue <pure.logic@nexus-software.ie>
Cc: John Youn <John.Youn@synopsys.com>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH] usb: dwc3: gadget: Init only available HW eps
Date: Fri, 08 Jan 2021 14:23:22 +0200	[thread overview]
Message-ID: <87eeivwrb9.fsf@kernel.org> (raw)
In-Reply-To: <19b685a9-0c25-9b6c-ecaf-ffca4069182b@synopsys.com>

[-- Attachment #1: Type: text/plain, Size: 1968 bytes --]


Hi,

Thinh Nguyen <Thinh.Nguyen@synopsys.com> writes:
>>>>> How have you verified this patch? Did you read Bryan's commit log? This
>>>>> is likely to reintroduce the problem raised by Bryan.
>>>>>
>>>> We verified with our FPGA HAPS with various number of endpoints. No
>>>> issue is seen.
>>> That's cool. Could you please make sure our understanding of this is
>>> sound and won't interfere with any designs? If we modify this part of
>>> the code again, I'd like to see a clear reference to a specific section
>>> of the databook detailing the expected behavior :-)
>>>
>>> cheers
>>>
>> Hm... I didn't consider bidirection endpoint other than control endpoint.
>>
>> DWC3_USB3x_NUM_EPS specifies the number of device mode for single
>> directional endpoints. A bidirectional endpoint needs 2 single
>> directional endpoints, 1 IN and 1 OUT. So, if your setup uses 3
>> bidirection endpoints and only those, DWC3_USB3x_NUM_EPS should be 6.
>> DWC3_USB3x_NUM_IN_EPS specifies the maximum number of IN endpoint active
>> at any time.
>>
>> However, I will have to double check and confirm internally regarding
>> how to determine many endpoint would be available if bidirection
>> endpoints come into play.
>>
>> Thanks for pointing this out. Will get back on this.
>>
>> Thinh
>>
>
> Ok. Just had some discussion internally. So, like you said, any endpoint
> can be configured in either direction. However, we are limited to
> configuring up to DWC_USB3x_NUM_IN_EPS because each IN endpoint has its
> own TxFIFO while for OUT, they share the same RxFIFO. So we could have
> up to DWC_USB3x_NUM_EPS number of OUT endpoints. So, the issue Bryan
> attempted to address is still there.
>
> However, the current code still has some assumption on the number of IN
> and OUT endpoints, I need to think of a better solution.

Yes, the assumption still exists because at the time there was no better
solution :-)

-- 
balbi

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 857 bytes --]