From mboxrd@z Thu Jan  1 00:00:00 1970
From: Benjamin Poirier <benjamin.poirier@gmail.com>
Subject: Re: [PATCH RESEND] net: can: Introduce MEN 16Z192-00 CAN controller
 driver
Date: Mon, 8 Aug 2016 20:23:55 -0700
Message-ID: <20160809032355.fzbdpudsqg2bdn27@f1.synalogic.ca>
References: <20160726091555.GA26227@awelinux>
 <20160808035814.ulqx4hnbtkkd2iko@f1.synalogic.ca>
 <20160808072620.GA5749@awelinux>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <linux-kernel-owner@vger.kernel.org>
Content-Disposition: inline
In-Reply-To: <20160808072620.GA5749@awelinux>
Sender: linux-kernel-owner@vger.kernel.org
To: Andreas Werner <andreas.werner@men.de>
Cc: wg@grandegger.com, mkl@pengutronix.de, linux-can@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, davem@davemloft.net, jthumshirn@suse.de, andy@wernerandy.de
List-Id: linux-can.vger.kernel.org

On 2016/08/08 09:26, Andreas Werner wrote:
[...]
> > > +
> > > +	if (cf->can_dlc > 0)
> > > +		data[0] = be32_to_cpup((__be32 *)(cf->data));
> > > +	if (cf->can_dlc > 3)
> > > +		data[1] = be32_to_cpup((__be32 *)(cf->data + 4));
> > > +
> > > +	writel(id, &cf_buf->can_id);
> > > +	writel(cf->can_dlc, &cf_buf->length);
> > > +
> > > +	if (!(cf->can_id & CAN_RTR_FLAG)) {
> > > +		writel(data[0], &cf_buf->data[0]);
> > > +		writel(data[1], &cf_buf->data[1]);
> > > +
> > > +		stats->tx_bytes += cf->can_dlc;
> > > +	}
> > > +
> > > +	/* be sure everything is written to the
> > > +	 * device before acknowledge the data.
> > > +	 */
> > > +	mmiowb();
> > > +
> > > +	/* trigger the transmission */
> > > +	men_z192_ack_tx_pkg(priv, 1);
> > > +
> > > +	stats->tx_packets++;
> > > +
> > > +	kfree_skb(skb);
> > 
> > What prevents the skb data to be freed/reused before the device has
> > accessed it?

I'm sorry, I hadn't realized that all of the data (all 8 bytes of it!)
is written directly to the device. I was thinking about ethernet devices
that dma packet data.