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

From: Jeaho Hwang <jhhwang@rtst.co.kr>
To: Peter Chen <peter.chen@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: "Linux team" <team-linux@rtst.co.kr>,
	"변무광(Byeon Moo Kwang)/자동화연)Automation Platform연구팀"
	<mkbyeon@lselectric.co.kr>,
	"최기홍(Choi Ki Hong)/자동화연)Automation Platform연구팀"
	<khchoib@lselectric.co.kr>
Subject: Re: [PATCH v2] usb: chipidea: add loop timeout for hw_ep_set_halt()
Date: Tue, 24 Aug 2021 17:31:44 +0900	[thread overview]
Message-ID: <CAJk_X9gbnx5edLmxKUfZYyDMQYKeotO3undgQygmp1skn2HjSQ@mail.gmail.com> (raw)
In-Reply-To: <20210817064353.GA669425@ubuntu>

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.
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.

> Signed-off-by: Jeaho Hwang <jhhwang@rtst.co.kr>
>
> diff --git a/drivers/usb/chipidea/udc.c b/drivers/usb/chipidea/udc.c
> index 8834ca613721..d73fadb18f32 100644
> --- a/drivers/usb/chipidea/udc.c
> +++ b/drivers/usb/chipidea/udc.c
> @@ -209,6 +209,9 @@ static int hw_ep_prime(struct ci_hdrc *ci, int num, int dir, int is_ctrl)
>         return 0;
>  }
>
> +/* enough for zynq7000 evaluation board */
> +#define HW_EP_SET_HALT_COUNT_MAX 100
> +
>  /**
>   * hw_ep_set_halt: configures ep halt & resets data toggle after clear (execute
>   *                 without interruption)
> @@ -221,6 +224,7 @@ static int hw_ep_prime(struct ci_hdrc *ci, int num, int dir, int is_ctrl)
>   */
>  static int hw_ep_set_halt(struct ci_hdrc *ci, int num, int dir, int value)
>  {
> +       int count = HW_EP_SET_HALT_COUNT_MAX;
>         if (value != 0 && value != 1)
>                 return -EINVAL;
>
> @@ -232,9 +236,9 @@ static int hw_ep_set_halt(struct ci_hdrc *ci, int num, int dir, int value)
>                 /* data toggle - reserved for EP0 but it's in ESS */
>                 hw_write(ci, reg, mask_xs|mask_xr,
>                           value ? mask_xs : mask_xr);
> -       } while (value != hw_ep_get_halt(ci, num, dir));
> +       } while (value != hw_ep_get_halt(ci, num, dir) && --count > 0);
>
> -       return 0;
> +       return count ? 0 : -EAGAIN;
>  }
>
>  /**
> --
> 2.25.1
>