linux-kernel - Re: [PATCH v7 10/30] net: wan: Add support for QMC HDLC

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Date:   Mon, 9 Oct 2023 16:26:32 +0200
From:   Herve Codina <herve.codina@...tlin.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew@...n.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Qiang Zhao <qiang.zhao@....com>, Li Yang <leoyang.li@....com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Shengjiu Wang <shengjiu.wang@...il.com>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        Fabio Estevam <festevam@...il.com>,
        Nicolin Chen <nicoleotsuka@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Randy Dunlap <rdunlap@...radead.org>, netdev@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, alsa-devel@...a-project.org,
        Simon Horman <horms@...nel.org>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v7 10/30] net: wan: Add support for QMC HDLC

Hi Jakub,

On Fri, 6 Oct 2023 14:47:02 -0700
Jakub Kicinski <kuba@...nel.org> wrote:

> On Thu, 28 Sep 2023 09:06:28 +0200 Herve Codina wrote:
> > +static int qmc_hdlc_close(struct net_device *netdev)
> > +{
> > +	struct qmc_hdlc *qmc_hdlc = netdev_to_qmc_hdlc(netdev);
> > +	struct qmc_hdlc_desc *desc;
> > +	int i;
> > +
> > +	netif_stop_queue(netdev);
> > +
> > +	qmc_chan_stop(qmc_hdlc->qmc_chan, QMC_CHAN_ALL);
> > +	qmc_chan_reset(qmc_hdlc->qmc_chan, QMC_CHAN_ALL);  
> 
> stopping the queue looks a bit racy, a completion may come in 
> and restart the queue

Indeed, qmc_hdlc_xmit_complete() completion can restart the queue.

I will call netif_stop_queue() after calling qmc_chan_stop/reset().
This is the simple way to fix that without adding an internal flag.

Thanks for pointing that.

Best regards,
Hervé

> 
> > +	for (i = 0; i < ARRAY_SIZE(qmc_hdlc->tx_descs); i++) {
> > +		desc = &qmc_hdlc->tx_descs[i];
> > +		if (!desc->skb)
> > +			continue;
> > +		dma_unmap_single(qmc_hdlc->dev, desc->dma_addr, desc->dma_size,
> > +				 DMA_TO_DEVICE);
> > +		kfree_skb(desc->skb);
> > +		desc->skb = NULL;
> > +	}
> > +
> > +	for (i = 0; i < ARRAY_SIZE(qmc_hdlc->rx_descs); i++) {
> > +		desc = &qmc_hdlc->rx_descs[i];
> > +		if (!desc->skb)
> > +			continue;
> > +		dma_unmap_single(qmc_hdlc->dev, desc->dma_addr, desc->dma_size,
> > +				 DMA_FROM_DEVICE);
> > +		kfree_skb(desc->skb);
> > +		desc->skb = NULL;
> > +	}
> > +
> > +	hdlc_close(netdev);