netdev - Re: [PATCH] can: mcba_usb: Fix termination command argument

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Date:   Thu, 24 Nov 2022 18:50:52 +0900
From:   Yasushi SHOJI <yasushi.shoji@...il.com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     Remigiusz Kołłątaj 
        <remigiusz.kollataj@...ica.com>,
        Yasushi SHOJI <yashi@...cecubics.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] can: mcba_usb: Fix termination command argument

Hi,

On Thu, Nov 24, 2022 at 7:34 AM Marc Kleine-Budde <mkl@...gutronix.de> wrote:
>
> Let's take the original driver author into the loop.
>
> On 24.11.2022 04:44:06, Yasushi SHOJI wrote:
> > Microchip USB Analyzer can be set with termination setting ON or OFF.
> > As I've observed, both with my oscilloscope and USB packet capture
> > below, you must send "0" to turn it ON, and "1" to turn it OFF.
> >
> > Reverse the argument value to fix this.
> >
> > These are the two commands sequence, ON then OFF.
> >
> > > No.     Time           Source                Destination           Protocol Length Info
> > >       1 0.000000       host                  1.3.1                 USB      46     URB_BULK out
> > >
> > > Frame 1: 46 bytes on wire (368 bits), 46 bytes captured (368 bits)
> > > USB URB
> > > Leftover Capture Data: a80000000000000000000000000000000000a8
> > >
> > > No.     Time           Source                Destination           Protocol Length Info
> > >       2 4.372547       host                  1.3.1                 USB      46     URB_BULK out
> > >
> > > Frame 2: 46 bytes on wire (368 bits), 46 bytes captured (368 bits)
> > > USB URB
> > > Leftover Capture Data: a80100000000000000000000000000000000a9
>
> Is this the USB data after applying the patch?

That's not from Linux.

> Can you measure the resistance between CAN-H and CAN-L to verify that
> your patch fixes the problem?

Sure.  The command I'm using on my Linux is:

    sudo ip link set can0 up type can bitrate 100000 termination X

where X is either 0 or 120.

With Debian Sid stock kernel: linux-image-6.0.0-4-amd64
  - termination 0: 135.4 Ohms
  - termination 120: 17.82 Ohms

With my patch on v6.1-rc6
  - termination 0: 22.20 Ohms
  - termination 120: 134.2 Ohms

> > Signed-off-by: Yasushi SHOJI <yashi@...cecubics.com>
> > ---
> >  drivers/net/can/usb/mcba_usb.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/can/usb/mcba_usb.c b/drivers/net/can/usb/mcba_usb.c
> > index 218b098b261d..67beff1a3876 100644
> > --- a/drivers/net/can/usb/mcba_usb.c
> > +++ b/drivers/net/can/usb/mcba_usb.c
> > @@ -785,9 +785,9 @@ static int mcba_set_termination(struct net_device *netdev, u16 term)
> >       };
> >
> >       if (term == MCBA_TERMINATION_ENABLED)
> > -             usb_msg.termination = 1;
> > -     else
> >               usb_msg.termination = 0;
> > +     else
> > +             usb_msg.termination = 1;
> >
> >       mcba_usb_xmit_cmd(priv, (struct mcba_usb_msg *)&usb_msg);
>
> What about the static void mcba_usb_process_ka_usb() function? Do you
> need to convert this, too?

Ah, yes. Thanks.
Attaching a compressed patch.

Let me know if I need to resend it as an email.

Best,
--
          yashi

Download attachment "0001-can-mcba_usb-Fix-termination-command-argument.patch.gz" of type "application/gzip" (995 bytes)