linux-kernel - RE: [PATCH v7 1/2] can: xilinx CAN controller support

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Date:	Tue, 22 Apr 2014 11:18:48 +0000
From:	Appana Durga Kedareswara Rao <appana.durga.rao@...inx.com>
To:	Marc Kleine-Budde <mkl@...gutronix.de>
CC:	"linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Michal Simek <michals@...inx.com>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"wg@...ndegger.com" <wg@...ndegger.com>
Subject: RE: [PATCH v7 1/2] can: xilinx CAN controller support

Hi Marc,

> -----Original Message-----
> From: Marc Kleine-Budde [mailto:mkl@...gutronix.de]
> Sent: Tuesday, April 22, 2014 4:42 PM
> To: Appana Durga Kedareswara Rao
> Cc: linux-can@...r.kernel.org; netdev@...r.kernel.org; linux-arm-
> kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
> devicetree@...r.kernel.org; Michal Simek; robh+dt@...nel.org;
> grant.likely@...aro.org; wg@...ndegger.com
> Subject: Re: [PATCH v7 1/2] can: xilinx CAN controller support
>
> On 04/22/2014 01:08 PM, Appana Durga Kedareswara Rao wrote:
> > Hi Marc,
> >
> >> -----Original Message-----
> >> From: Marc Kleine-Budde [mailto:mkl@...gutronix.de]
> >> Sent: Tuesday, April 22, 2014 3:57 PM
> >> To: Appana Durga Kedareswara Rao; wg@...ndegger.com; Michal Simek;
> >> grant.likely@...aro.org; robh+dt@...nel.org
> >> Cc: linux-can@...r.kernel.org; netdev@...r.kernel.org; linux-arm-
> >> kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
> >> devicetree@...r.kernel.org
> >> Subject: Re: [PATCH v7 1/2] can: xilinx CAN controller support
> >>
> >> On 04/22/2014 12:06 PM, Appana Durga Kedareswara Rao wrote:
> >>
> >>>> Meanwhile Thomas Gleixner put some effort into the c_can driver and
> >>>> found some problems in most of the can driver. See comments inline.
> >>>>
> >>> Ok will look into that patches
> >>
> >> I've commented the relevant parts of your patch. Although more
> >> background information can be found in the c_can patches.
> >>
> > Ok
> >
> >>>>> +/**
> >>>>> + * xcan_tx_interrupt - Tx Done Isr
> >>>>> + * @ndev:  net_device pointer
> >>>>> + * @isr:   Interrupt status register value
> >>>>> + */
> >>>>> +static void xcan_tx_interrupt(struct net_device *ndev, u32 isr) {
> >>>>> +   struct xcan_priv *priv = netdev_priv(ndev);
> >>>>> +   struct net_device_stats *stats = &ndev->stats;
> >>>>> +
> >>>>> +   while (priv->tx_head - priv->tx_tail > 0) {
> >>>>> +           priv->write_reg(priv, XCAN_ICR_OFFSET,
> >>>> XCAN_IXR_TXOK_MASK);
> >>>>> +           if (!(isr & XCAN_IXR_TXOK_MASK))
> >>>>> +                   break;
> >>>>
> >>>> This looks broken. I assume you have to issue the
> >> XCAN_IXR_TXOK_MASK-
> >>>> write once per tx-completed CAN frame. If you enter this loop you
> >>>> write once, then isr is read, then you write again and may exit
> >>>> this loop if XCAN_IXR_TXOK_MASK is not set anymore.
> >>
> >> Let's assume you have put 3 CAN frames into the TX-queue and we're
> >> into tx-complete interrupt for the first frame and the other 2 are
> >> still not completed.
> >>
> >> This means the while() loop is not terminated by (priv->tx_head -
> >> priv->tx_tail > 0), as it can loop 3 times.
> >>
> >> What happens is:
> >>
> >> - priv->write_reg(priv, XCAN_ICR_OFFSET, XCAN_IXR_TXOK_MASK);
> >> - if (!(isr & XCAN_IXR_TXOK_MASK)) -> no break
> >> - can_get_echo_skb()
> >> - ...
> >> - isr = priv->read_reg(priv, XCAN_ISR_OFFSET);
> >> - loop ->
> >> - priv->write_reg(priv, XCAN_ICR_OFFSET, XCAN_IXR_TXOK_MASK);
> >> - if (!(isr & XCAN_IXR_TXOK_MASK)) -> break
> >>
> >> So you have 2x write_reg(priv, XCAN_ICR_OFFSET,
> XCAN_IXR_TXOK_MASK),
> >> but only a single TX completed CAN frame.
> >>
> >
> > Ok now got it :). Thanks for the explanation.
> > Will modify the loop logic like below.
> >
> > while (priv->tx_head - priv->tx_tail > 0) {
> >                  if ((isr & XCAN_IXR_TXOK_MASK)) {
> >                 priv->write_reg(priv, XCAN_ICR_OFFSET, XCAN_IXR_TXOK_MASK);
> >                         can_get_echo_skb(ndev, priv->tx_tail %
> >                                                 priv->tx_max);
> >                         priv->tx_tail++;
> >                         stats->tx_packets++;
> >                 } else {
> >                 break;
> >         }
> >
> >   }
> > Are you ok with this?
>
> what about this:
>
> while ((priv->tx_head - priv->tx_tail > 0) &&
>       (isr & XCAN_IXR_TXOK_MASK)) {
>
>       [...]
>
>       isr = priv->read_reg(priv, XCAN_ISR_OFFSET); }
>
> or even
>
> while ((priv->tx_head - priv->tx_tail > 0) &&
>       (priv->read_reg(priv, XCAN_ISR_OFFSET) & XCAN_IXR_TXOK_MASK))
> {
>
>       [...]
>
> }
Ok will use any one of the above.


Regards,
Kedar.

>
> Marc
>
> --
> Pengutronix e.K.                  | Marc Kleine-Budde           |
> Industrial Linux Solutions        | Phone: +49-231-2826-924     |
> Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
> Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |



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