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Date:   Fri, 28 Jan 2022 12:23:33 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Oleksij Rempel <o.rempel@pengutronix.de>
Cc:     Oliver Neukum <oneukum@suse.com>, netdev@vger.kernel.org,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel@pengutronix.de, Jakub Kicinski <kuba@kernel.org>,
        "David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH net-next v1 1/1] usbnet: add devlink support
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References: <20220127110742.922752-1-o.rempel@pengutronix.de>
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On Fri, Jan 28, 2022 at 12:12:38PM +0100, Oleksij Rempel wrote:
> On Thu, Jan 27, 2022 at 02:22:49PM +0100, Greg KH wrote:
> > On Thu, Jan 27, 2022 at 01:31:52PM +0100, Oleksij Rempel wrote:
> > > On Thu, Jan 27, 2022 at 12:13:53PM +0100, Greg KH wrote:
> > > > On Thu, Jan 27, 2022 at 12:07:42PM +0100, Oleksij Rempel wrote:
> > > > > The weakest link of usbnet devices is the USB cable.
> > > > 
> > > > The weakest link of any USB device is the cable, why is this somehow
> > > > special to usbnet devices?
> > > > 
> > > > > Currently there is
> > > > > no way to automatically detect cable related issues except of analyzing
> > > > > kernel log, which would differ depending on the USB host controller.
> > > > > 
> > > > > The Ethernet packet counter could potentially show evidence of some USB
> > > > > related issues, but can be Ethernet related problem as well.
> > > > > 
> > > > > To provide generic way to detect USB issues or HW issues on different
> > > > > levels we need to make use of devlink.
> > > > 
> > > > Please make this generic to all USB devices, usbnet is not special here
> > > > at all.
> > > 
> > > Ok. I'll need some help. What is the best place to attach devlink
> > > registration in the USB subsystem and the places to attach health
> > > reporters?
> > 
> > You tell us, you are the one that thinks this needs to be reported to
> > userspace. What is only being reported in kernel logs that userspace
> > somehow needs to see?  And what will userspace do with that information?
> 
> The user space should get an event in case there is a problem with the
> USB transfers, i.e. the URB status is != 0.

That's pretty brave, lots of things can have a urb status of != 0 in
semi-normal operation, have you tried this?

> The use space then can decide if the USB device needs to be reset, power
> cycled and so on.
> 
> What about calling a to-be-written devlink function that reports the USB
> status if the URB status is not 0:
> 
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index d0f45600b669..a90134854f32 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -1648,6 +1648,8 @@ static void __usb_hcd_giveback_urb(struct urb *urb)
>  	usb_unanchor_urb(urb);
>  	if (likely(status == 0))
>  		usb_led_activity(USB_LED_EVENT_HOST);
> +	else
> +		devlink_report_usb_status(urb, status);

Try it and do lots of transfers, device additions and removals and other
things and let us know what it reports.

thanks,

greg k-h