linux-kernel - Re: [PATCH v2] usb: chipidea: add loop timeout for hw_ep_set

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Date:   Sat, 28 Aug 2021 09:38:11 +0800
From:   Peter Chen <peter.chen@...nel.org>
To:     Jeaho Hwang <jhhwang@...t.co.kr>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linux team <team-linux@...t.co.kr>,
        변무광(Byeon Moo Kwang)/자동화연)Automation Platform연구팀 
        <mkbyeon@...lectric.co.kr>,
        최기홍(Choi Ki Hong)/자동화연)Automation Platform연구팀 
        <khchoib@...lectric.co.kr>
Subject: Re: [PATCH v2] usb: chipidea: add loop timeout for hw_ep_set_halt()

On 21-08-27 10:35:05, Jeaho Hwang wrote:
> 2021년 8월 27일 (금) 오전 8:08, Peter Chen <peter.chen@...nel.org>님이 작성:
> >
> > On 21-08-24 17:31:44, Jeaho Hwang wrote:
> > > 2021년 8월 17일 (화) 오후 3:44, Jeaho Hwang <jhhwang@...t.co.kr>님이 작성:
> > > >
> > > > If ctrl EP priming is failed (very rare case in standard linux),
> > > > hw_ep_set_halt goes infinite loop. waiting 100 times was enough
> > > > for zynq7000.
> > > >
> > >
> > > Hi Peter.
> > > I found from zynq7000 TRM that the hardware clears Stall bit if a
> > > setup packet is received on a control endpoint.
> > > I think hw_ep_set_halt goes infinite loop since:
> > >
> > > 1. hw_ep_prime for control EP which is called from
> > > isr_tr_complete_handler -> isr_setup_status_phase is failed due to a
> > > setup packet received.
> >
> > How do you know that? Do you observe the new setup packet on the bus
> > before the current status stage? Usually, the host doesn't begin new setup
> > transfer before current setup transfer has finished.
> >
> > Peter
> >
> 
> I found an error return from the second ENDPTSETUPSTAT checking
> routine, then setting the stall bit(TXS) kept failing. So I guessed it
> is due to a setup packet received.
> I didn't observe the setup packet by e.g. HW probes. Any other reason
> to produce that symptom?

I guess two possible reasons for that:
- The new setup is coming after priming
- The interrupt occurs after prime, and when the back from interrupt,
other thread for USB transfer is scheduled, eg, usb_ep_queue from RNDIS 

>From your experiments and observation, it seems the first reason is not possible.
Did your get failure with UP system?

Peter

> 
> For reminder, only reproduced on preemp_rt kernel and with Windows(10)
> RNDIS host.
> 
> thanks.
> 
>  191 static int hw_ep_prime(struct ci_hdrc *ci, int num, int dir, int is_ctrl)
>  192 {
>  193     int n = hw_ep_bit(num, dir);
>  194
>  195     /* Synchronize before ep prime */
>  196     wmb();
>  197
>  198     if (is_ctrl && dir == RX && hw_read(ci, OP_ENDPTSETUPSTAT, BIT(num)))
>  199         return -EAGAIN;
>  200
>  201     hw_write(ci, OP_ENDPTPRIME, ~0, BIT(n));
>  202
>  203     while (hw_read(ci, OP_ENDPTPRIME, BIT(n)))
>  204         cpu_relax();
>  205     if (is_ctrl && dir == RX && hw_read(ci, OP_ENDPTSETUPSTAT, BIT(num)))
>  206         return -EAGAIN;
>              ~~~~~~~~~~~~~~~~
>  207
>  208     /* status shoult be tested according with manual but it doesn't work */
>  209     return 0;
>  210 }
> 
> > > 2. in isr_tr_complete_handler it tries to call _ep_set_halt if either
> > > isr_tr_complete_low or isr_setup_status_phase returns error.
> > > 3. Since the control EP got a setup packet, HW resets TXS bit just as
> > > the driver sets inside hw_ep_set_halt so it goes infinite loop.
> > >
> > > Does it make sense? If it is right, we shouldn't call _ep_set_halt if
> > > the err is -EAGAIN, which could be returned ONLY due to the setup
> > > packet issue described above.
> > > And the loop timeout is not required anymore.
> > >
> > > Can I ask your opinion on this, Peter and USB experts?
> > >
> > > Thanks.
> > >

-- 

Thanks,
Peter Chen