linux-kernel - Re: [PATCH v2][RESEND] usb: gadget: core: Fix ->udc_set

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Date:   Wed, 1 Nov 2017 10:24:54 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Roger Quadros <rogerq@...com>
cc:     balbi@...nel.org, <Dylan.Howey@...nantco.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "# v4 . 13+" <stable@...r.kernel.org>
Subject: Re: [PATCH v2][RESEND] usb: gadget: core: Fix ->udc_set_speed()
 speed handling

On Tue, 31 Oct 2017, Roger Quadros wrote:

> Currently UDC core calls ->udc_set_speed() with the speed parameter
> containing the maximum speed supported by the gadget function
> driver. This might very well be more than that supported by the
> UDC controller driver.
> 
> Select the lesser of the 2 speeds so both UDC and gadget function
> driver are operating within limits.
> 
> This fixes PHY Erratic errors and 2 second enumeration delay on
> TI's AM437x platforms.
> 
> Fixes: 6099eca796ae ("usb: gadget: core: introduce ->udc_set_speed() method")
> Cc: <stable@...r.kernel.org> # v4.13+
> Reported-by: Dylan Howey <Dylan.Howey@...nantco.com>
> Signed-off-by: Roger Quadros <rogerq@...com>
> ---
> v2:
> - Move speed limiting code to UDC core.
> 
>  drivers/usb/gadget/udc/core.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
> index d41d07a..def1b05 100644
> --- a/drivers/usb/gadget/udc/core.c
> +++ b/drivers/usb/gadget/udc/core.c
> @@ -1080,8 +1080,12 @@ static inline void usb_gadget_udc_stop(struct usb_udc *udc)
>  static inline void usb_gadget_udc_set_speed(struct usb_udc *udc,
>  					    enum usb_device_speed speed)
>  {
> -	if (udc->gadget->ops->udc_set_speed)
> -		udc->gadget->ops->udc_set_speed(udc->gadget, speed);
> +	if (udc->gadget->ops->udc_set_speed) {
> +		enum usb_device_speed s;
> +
> +		s = min(speed, udc->gadget->max_speed);
> +		udc->gadget->ops->udc_set_speed(udc->gadget, s);
> +	}
>  }
>  
>  /**

Roger, would you like to send in a follow-up patch that removes the now 
unnecessary code from dummy_udc_set_speed() in dummy_hcd.c?

Alan Stern