Re: [PATCH v2] usb: chipidea: add loop timeout for hw_ep_set_halt()

Peter Chen
2021-08-28T01:38:27Z

On 21-08-27 10:35:05, Jeaho Hwang wrote:
> 2021년 8월 27일 (금) 오전 8:08, Peter Chen <peter.chen@kernel.org>님이 작성:
> >
> > On 21-08-24 17:31:44, Jeaho Hwang wrote:
> > > 2021년 8월 17일 (화) 오후 3:44, Jeaho Hwang <jhhwang@rtst.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