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Tue, 21 Oct 2025 06:15:28 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHtT4dHlzzmepxbEEmjHJkJHD2FwCKCqSVsiJy1urptxBGYwBKtZyQJidvDZgwFYhtUThLA/A== X-Received: by 2002:a05:6000:4013:b0:3d1:61f0:d26c with SMTP id ffacd0b85a97d-42704dce7bdmr12202091f8f.54.1761052528186; Tue, 21 Oct 2025 06:15:28 -0700 (PDT) Received: from fedora ([2a01:e0a:257:8c60:80f1:cdf8:48d0:b0a1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4731c95efb9sm164559345e9.8.2025.10.21.06.15.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Oct 2025 06:15:27 -0700 (PDT) Date: Tue, 21 Oct 2025 15:15:24 +0200 From: Matias Ezequiel Vara Larsen To: Francesco Valla Cc: Marc Kleine-Budde , Paolo Abeni , Harald Mommer , Mikhail Golubev-Ciuchea , Wolfgang Grandegger , Eric Dumazet , Jakub Kicinski , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , Damir Shaikhutdinov , linux-kernel@vger.kernel.org, linux-can@vger.kernel.org, netdev@vger.kernel.org, virtualization@lists.linux.dev, development@redaril.me Subject: Re: [PATCH v5] can: virtio: Initial virtio CAN driver. Message-ID: References: <20240108131039.2234044-1-Mikhail.Golubev-Ciuchea@opensynergy.com> <27327622.1r3eYUQgxm@fedora.fritz.box> <28156189.1r3eYUQgxm@fedora.fritz.box> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <28156189.1r3eYUQgxm@fedora.fritz.box> On Tue, Oct 21, 2025 at 02:08:35PM +0200, Francesco Valla wrote: > On Tuesday, 21 October 2025 at 11:40:07 Matias Ezequiel Vara Larsen wrote: > > On Mon, Oct 20, 2025 at 11:24:15PM +0200, Francesco Valla wrote: > > > On Monday, 20 October 2025 at 16:56:08 Matias Ezequiel Vara Larsen wrote: > > > > On Tue, Oct 14, 2025 at 06:01:07PM +0200, Francesco Valla wrote: > > > > > On Tuesday, 14 October 2025 at 12:15:12 Matias Ezequiel Vara Larsen wrote: > > > > > > On Thu, Sep 11, 2025 at 10:59:40PM +0200, Francesco Valla wrote: > > > > > > > Hello Mikhail, Harald, > > > > > > > > > > > > > > hoping there will be a v6 of this patch soon, a few comments: > > > > > > > > > > > > > > On Monday, 8 January 2024 at 14:10:35 Mikhail Golubev-Ciuchea wrote: > > > > > > > > > > > > > > [...] > > > > > > > > + > > > > > > > > +/* Compare with m_can.c/m_can_echo_tx_event() */ > > > > > > > > +static int virtio_can_read_tx_queue(struct virtqueue *vq) > > > > > > > > +{ > > > > > > > > + struct virtio_can_priv *can_priv = vq->vdev->priv; > > > > > > > > + struct net_device *dev = can_priv->dev; > > > > > > > > + struct virtio_can_tx *can_tx_msg; > > > > > > > > + struct net_device_stats *stats; > > > > > > > > + unsigned long flags; > > > > > > > > + unsigned int len; > > > > > > > > + u8 result; > > > > > > > > + > > > > > > > > + stats = &dev->stats; > > > > > > > > + > > > > > > > > + /* Protect list and virtio queue operations */ > > > > > > > > + spin_lock_irqsave(&can_priv->tx_lock, flags); > > > > > > > > + > > > > > > > > + can_tx_msg = virtqueue_get_buf(vq, &len); > > > > > > > > + if (!can_tx_msg) { > > > > > > > > + spin_unlock_irqrestore(&can_priv->tx_lock, flags); > > > > > > > > + return 0; /* No more data */ > > > > > > > > + } > > > > > > > > + > > > > > > > > + if (unlikely(len < sizeof(struct virtio_can_tx_in))) { > > > > > > > > + netdev_err(dev, "TX ACK: Device sent no result code\n"); > > > > > > > > + result = VIRTIO_CAN_RESULT_NOT_OK; /* Keep things going */ > > > > > > > > + } else { > > > > > > > > + result = can_tx_msg->tx_in.result; > > > > > > > > + } > > > > > > > > + > > > > > > > > + if (can_priv->can.state < CAN_STATE_BUS_OFF) { > > > > > > > > + /* Here also frames with result != VIRTIO_CAN_RESULT_OK are > > > > > > > > + * echoed. Intentional to bring a waiting process in an upper > > > > > > > > + * layer to an end. > > > > > > > > + * TODO: Any better means to indicate a problem here? > > > > > > > > + */ > > > > > > > > + if (result != VIRTIO_CAN_RESULT_OK) > > > > > > > > + netdev_warn(dev, "TX ACK: Result = %u\n", result); > > > > > > > > > > > > > > Maybe an error frame reporting CAN_ERR_CRTL_UNSPEC would be better? > > > > > > > > > > > > > I am not sure. In xilinx_can.c, CAN_ERR_CRTL_UNSPEC is indicated during > > > > > > a problem in the rx path and this is the tx path. I think the comment > > > > > > refers to improving the way the driver informs this error to the user > > > > > > but I may be wrong. > > > > > > > > > > > > > > > > Since we have no detail of what went wrong here, I suggested > > > > > CAN_ERR_CRTL_UNSPEC as it is "unspecified error", to be coupled with a > > > > > controller error with id CAN_ERR_CRTL; however, a different error might be > > > > > more appropriate. > > > > > > > > > > For sure, at least in my experience, having a warn printed to kmsg is *not* > > > > > enough, as the application sending the message(s) would not be able to detect > > > > > the error. > > > > > > > > > > > > > > > > > For sure, counting the known errors as valid tx_packets and tx_bytes > > > > > > > is misleading. > > > > > > > > > > > > > > > > > > > I'll remove the counters below. > > > > > > > > > > > > > > > > We don't really know what's wrong here - the packet might have been sent and > > > > > and then not ACK'ed, as well as any other error condition (as it happens in the > > > > > reference implementation from the original authors [1]). Echoing the packet > > > > > only "to bring a waiting process in an upper layer to an end" and incrementing > > > > > counters feels wrong, but maybe someone more expert than me can advise better > > > > > here. > > > > > > > > > > > > > > > > > > I agree. IIUC, in case there has been a problem during transmission, I > > > > should 1) indicate this by injecting a CAN_ERR_CRTL_UNSPEC package with > > > > netif_rx() and 2) use can_free_echo_skb() and increment the tx_error > > > > stats. Is this correct? > > > > > > > > Matias > > > > > > > > > > > > > > That's my understanding too! stats->tx_dropped should be the right value to > > > increment (see for example [1]). > > > > > > [1] https://elixir.bootlin.com/linux/v6.17.3/source/drivers/net/can/ctucanfd/ctucanfd_base.c#L1035 > > > > > > > I think the counter to increment would be stats->tx_errors in this case ... > > > > I don't fully agree. tx_errors is for CAN frames that got transmitted but then > lead to an error (e.g.: no ACK), while here we might be dealing with frames > that didn't even manage to reach the transmission queue [1]. > Let's use tx_dropped then, I honestly do not have an strong opinion about it. We can change that later if we are not happy. Matias