linux-kernel - Re: [PATCH V3] can: usb: f81604: add Fintek F81604 support

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Message-ID: <20230328062456.wjk5gj4vbriu7fzq@pengutronix.de>
Date:   Tue, 28 Mar 2023 08:24:56 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Vincent MAILHOL <mailhol.vincent@...adoo.fr>
Cc:     Peter Hong <peter_hong@...tek.com.tw>, wg@...ndegger.com,
        michal.swiatkowski@...ux.intel.com, Steen.Hegelund@...rochip.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, frank.jungclaus@....eu,
        linux-kernel@...r.kernel.org, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, hpeter+linux_kernel@...il.com
Subject: Re: [PATCH V3] can: usb: f81604: add Fintek F81604 support

On 28.03.2023 13:49:05, Vincent MAILHOL wrote:
[...]
> > >> +       int status, len;
> > >> +
> > >> +       if (can_dropped_invalid_skb(netdev, skb))
> > >> +               return NETDEV_TX_OK;
> > >> +
> > >> +       netif_stop_queue(netdev);
> > > In your driver, you send the CAN frames one at a time and wait for the
> > > rx_handler to restart the queue. This approach dramatically degrades
> > > the throughput. Is this a device limitation? Is the device not able to
> > > manage more than one frame at a time?
> > >
> >
> > This device will not NAK on TX frame not complete, it only NAK on TX
> > endpoint
> > memory not processed, so we'll send next frame unitl TX complete(TI)
> > interrupt
> > received.
> >
> > The device can polling status register via TX/RX endpoint, but it's more
> > complex.
> > We'll plan to do it when first driver landing in mainstream.
> 
> OK for me to have this as a next step. Marc, what do you think?

Fine with me. First make it work, then make it fast.

But I think this will never be a fast and resource-efficient USB CAN
adapter. There are exiting drivers with an open and documented USB
interface (gs_usb) and Open Source µC implementations (candlelight) with
better performance.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
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Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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