linux-kernel - Re: [PATCH] chipidea: Fix issue in reconnecing gadget without insmod/rmmod

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Date:   Wed, 12 Apr 2017 19:51:42 +0800
From:   Peter Chen <hzpeterchen@...il.com>
To:     Niranjan Dighe <niranjan.dighe@...il.com>
Cc:     Peter.Chen@...escale.com, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] chipidea: Fix issue in reconnecing gadget without
 insmod/rmmod

On Tue, Apr 11, 2017 at 08:46:24PM +0530, Niranjan Dighe wrote:
> Currently usb_gadget_connect() is called only through gadget
> registration via composite_driver_probe(). As a result, after a
> disconnection, if the role transitions to host and back to gadget,
> the gadget is not recognized by the host anymore.
> This is a typical scenario with an iAP device in the following
> usecase -
> conn iAP dev -> send roleswitch command -> roleswitch ourself
> to gadget -> disconnect iAP device -> roleswitch back to host to
> enumerate the device again -> reconnect device -> resend the
> roleswitch command -> roleswitch ourself to gadget -> ISSUE.
> 
> To workaround this, do the following -
> 
> 1. Restart OTG FSM on SLi interrupt and on switching role to gadget
> so that device transitions to B_IDLE state from B_PERIPHERAL state.
> A transition from B_IDLE to B_PERIPHERAL is needed to enable
> interrups and restore the correct state of the chipidea controller
> so that communication with host is possible
> 
> 2. usb_gadget_connect() after roleswitch to gadget so that
> gadget->ops->pullup() is called and D+ line is asserted. This
> causes host to "see" the device and enumeration can happen.
> 
> Signed-off-by: Niranjan Dighe <niranjan.dighe@...il.com>
> ---
>  drivers/usb/chipidea/debug.c | 10 +++++++++-
>  drivers/usb/chipidea/udc.c   |  3 +++
>  2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/chipidea/debug.c b/drivers/usb/chipidea/debug.c
> index a4f7db2..66c1485 100644
> --- a/drivers/usb/chipidea/debug.c
> +++ b/drivers/usb/chipidea/debug.c
> @@ -16,7 +16,7 @@
>  #include "udc.h"
>  #include "bits.h"
>  #include "otg.h"
> -
> +extern void ci_hdrc_otg_fsm_restart(struct ci_hdrc *);
>  /**
>   * ci_device_show: prints information about device capabilities and status
>   */
> @@ -325,6 +325,14 @@ static ssize_t ci_role_write(struct file *file, const char __user *ubuf,
>  	ci_role_stop(ci);
>  	ret = ci_role_start(ci, role);
>  	enable_irq(ci->irq);
> +
> +	/* REVISIT - Avoid repeated FSM restart*/
> +
> +	if (role == CI_ROLE_GADGET) {
> +		ci_hdrc_otg_fsm_restart(ci);
> +		usb_gadget_connect(&ci->gadget);
> +	}
> +
>  	pm_runtime_put_sync(ci->dev);
>  
>  	return ret ? ret : count;
> diff --git a/drivers/usb/chipidea/udc.c b/drivers/usb/chipidea/udc.c
> index a0accd5..1e3b827 100644
> --- a/drivers/usb/chipidea/udc.c
> +++ b/drivers/usb/chipidea/udc.c
> @@ -29,6 +29,8 @@
>  #include "otg.h"
>  #include "otg_fsm.h"
>  
> +extern void ci_hdrc_otg_fsm_restart(struct ci_hdrc *);
> +
>  /* control endpoint description */
>  static const struct usb_endpoint_descriptor
>  ctrl_endpt_out_desc = {
> @@ -1881,6 +1883,7 @@ static irqreturn_t udc_irq(struct ci_hdrc *ci)
>  				ci->driver->suspend(&ci->gadget);
>  				usb_gadget_set_state(&ci->gadget,
>  						USB_STATE_SUSPENDED);
> +				ci_hdrc_otg_fsm_restart(ci);
>  				spin_lock(&ci->lock);
>  			}
>  		}
> -- 

Hi Niranjan,

When working with iAP device, there are two role-switch methods
- Through OTG FSM, and using sysfs entries under
/sys/bus/platform/devices/ci_hdrc.0/inputs
but you may need to patch code to keep vbus always on for A-device,
it is not compliance with OTG spec.
- Using role interface under debugfs (I move it under sysfs for v4.12).
But you need to patch the code and let the A-device switch back to
host after iAP is disconnected.

You don't need to use above two methods together, I suggest using the
2nd method since OTG FSM is hard to maintain due to no mandatory use
case for it.

-- 

Best Regards,
Peter Chen