netdev - Re: [virtio-dev] [RFC PATCH 1/1] can: virtio: Initial virtio CAN driver.

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Message-ID: <CAMZ6Rq+RjOHaGx-7GLsj-PNAcHd=nGd=JERddqw4FWbNN3sAXA@mail.gmail.com>
Date:   Sat, 5 Nov 2022 18:21:55 +0900
From:   Vincent Mailhol <vincent.mailhol@...il.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Harald Mommer <hmo@...nsynergy.com>,
        Harald Mommer <harald.mommer@...nsynergy.com>,
        virtio-dev@...ts.oasis-open.org, linux-can@...r.kernel.org,
        Netdev <netdev@...r.kernel.org>, linux-kernel@...r.kernel.org,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Dariusz Stojaczyk <Dariusz.Stojaczyk@...nsynergy.com>,
        Stratos Mailing List <stratos-dev@...lists.linaro.org>
Subject: Re: [virtio-dev] [RFC PATCH 1/1] can: virtio: Initial virtio CAN driver.

On Fry. 4 nov. 2022 at 20:13, Arnd Bergmann <arnd@...nel.org> wrote:
> On Thu, Nov 3, 2022, at 13:26, Harald Mommer wrote:
> > On 25.08.22 20:21, Arnd Bergmann wrote:
> >>
> ...
> > The messages are not necessarily processed in sequence by the CAN stack.
> > CAN is priority based. The lower the CAN ID the higher the priority. So
> > a message with CAN ID 0x100 can surpass a message with ID 0x123 if the
> > hardware is not just simple basic CAN controller using a single TX
> > mailbox with a FIFO queue on top of it.

Really? I acknowledge that it is priority based *on the bus*, i.e. if
two devices A and B on the same bus try to send CAN ID 0x100 and 0x123
at the same time, then device A will win the CAN arbitration.
However, I am not aware of any devices which reorder their own stack
according to the CAN IDs. If I first send CAN ID 0x123 and then ID
0x100 on the device stack, 0x123 would still go out first, right?

> > Thinking about this the code becomes more complex with the array. What I
> > get from the device when the message has been processed is a pointer to
> > the processed message by virtqueue_get_buf(). I can then simply do a
> > list_del(), free the message and done.
>
> Ok