linux-kernel - Re: [PATCH] usb: Increase quirk delay for USB devices

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Message-ID: <20170905202225.GC16996@roeck-us.net>
Date:   Tue, 5 Sep 2017 13:22:25 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Dmitry Fleytman <dmitry@...nix.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Johan Hovold <johan@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Eugene Korenevsky <ekorenevsky@...il.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: Increase quirk delay for USB devices

On Tue, Sep 05, 2017 at 11:40:56AM +0300, Dmitry Fleytman wrote:
> Commit e0429362ab15
> ("usb: Add device quirk for Logitech HD Pro Webcams C920 and C930e")
> introduced quirk to workaround an issue with some Logitech webcams.
> 
> The workaround is introducing delay for some USB operations.
> 
> According to our testing, delay introduced by original commit
> is not long enough and in rare cases we still see issues described
> by the aforementioned commit.
> 
> This patch increases delays introduced by original commit.
> Having this patch applied we do not see those problems anymore.
> 
> Signed-off-by: Dmitry Fleytman <dmitry@...nix.com>
> ---
>  drivers/usb/core/config.c | 2 +-
>  drivers/usb/core/hub.c    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
> index 4be52c6..854c8d6 100644
> --- a/drivers/usb/core/config.c
> +++ b/drivers/usb/core/config.c
> @@ -852,7 +852,7 @@ int usb_get_configuration(struct usb_device *dev)
>  		}
>  
>  		if (dev->quirks & USB_QUIRK_DELAY_INIT)
> -			msleep(100);
> +			msleep(200);

How did you determine the new delays ? Was it discussed with the vendor,
or is it based on trial and error ?

Either case, did you confirm that you need to increase both delays
for the problem to disappear ?

Thanks,
Guenter

>  
>  		result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno,
>  		    bigbuffer, length);
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 822f8c5..78c2aca 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -4825,7 +4825,7 @@ static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
>  			goto loop;
>  
>  		if (udev->quirks & USB_QUIRK_DELAY_INIT)
> -			msleep(1000);
> +			msleep(2000);
>  
>  		/* consecutive bus-powered hubs aren't reliable; they can
>  		 * violate the voltage drop budget.  if the new child has
> -- 
> 2.7.4
>