Date:	Wed, 13 Apr 2016 06:25:36 +0000
From:	Ramesh Shanmugasundaram <ramesh.shanmugasundaram@...renesas.com>
To:	"wg@...ndegger.com" <wg@...ndegger.com>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"corbet@....net" <corbet@....net>,
	"mkl@...gutronix.de" <mkl@...gutronix.de>
CC:	"linux-renesas-soc@...r.kernel.org" 
	<linux-renesas-soc@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"geert+renesas@...der.be" <geert+renesas@...der.be>,
	Chris Paterson <Chris.Paterson2@...esas.com>
Subject: RE: [PATCH v2] can: rcar_canfd: Add Renesas R-Car CAN FD driver

HI Marc,

Gentle reminder!
Are you happy with the open comment's disposition? I can send a next version of patch if we have a closure on current set of comments.

Thanks,
Ramesh

> -----Original Message-----
> From: Ramesh Shanmugasundaram
> Sent: 01 April 2016 13:49
> To: Ramesh Shanmugasundaram <ramesh.shanmugasundaram@...renesas.com>;
> wg@...ndegger.com; robh+dt@...nel.org; pawel.moll@....com;
> mark.rutland@....com; ijc+devicetree@...lion.org.uk; galak@...eaurora.org;
> corbet@....net
> Cc: linux-renesas-soc@...r.kernel.org; devicetree@...r.kernel.org; linux-
> can@...r.kernel.org; netdev@...r.kernel.org; linux-doc@...r.kernel.org;
> geert+renesas@...der.be; Chris Paterson <Chris.Paterson2@...esas.com>
> Subject: RE: [PATCH v2] can: rcar_canfd: Add Renesas R-Car CAN FD driver
> 
> Hi Marc,
> 
> Thanks for your time & review comments.
> 
> > -----Original Message-----
> (...)
> > > +#define RCANFD_NAPI_WEIGHT		8	/* Rx poll quota */
> > > +
> > > +#define RCANFD_NUM_CHANNELS		2
> > > +#define RCANFD_CHANNELS_MASK		0x3	/* Two channels max */
> >
> > (BIT(RCANFD_NUM_CHANNELS) - 1
> 
> OK
> 
> >
> > > +
> > > +/* Rx FIFO is a global resource of the controller. There are 8 such
> > FIFOs
> > > + * available. Each channel gets a dedicated Rx FIFO (i.e.) the
> > > + channel
> (...)
> > > +#define RCANFD_CMFIFO_CFDLC(x)		(((x) & 0xf) << 28)
> > > +#define RCANFD_CMFIFO_CFPTR(x)		(((x) & 0xfff) << 16)
> > > +#define RCANFD_CMFIFO_CFTS(x)		(((x) & 0xff) << 0)
> > > +
> > > +/* Global Test Config register */
> > > +#define RCANFD_GTSTCFG_C0CBCE		BIT(0)
> > > +#define RCANFD_GTSTCFG_C1CBCE		BIT(1)
> > > +
> > > +#define RCANFD_GTSTCTR_ICBCTME		BIT(0)
> > > +
> > > +/* AFL Rx rules registers */
> > > +#define RCANFD_AFLCFG_SETRNC0(x)	(((x) & 0xff) << 24)
> > > +#define RCANFD_AFLCFG_SETRNC1(x)	(((x) & 0xff) << 16)
> >
> > What about something like:
> >
> > #define RCANFD_AFLCFG_SETRNC(n, x)	(((x) & 0xff) << (24 - n * 8))
> >
> > This will save some if()s in the code
> 
> Nice :-). Will update.
> 
> >
> > > +#define RCANFD_AFLCFG_GETRNC0(x)	(((x) >> 24) & 0xff)
> > > +#define RCANFD_AFLCFG_GETRNC1(x)	(((x) >> 16) & 0xff)
> > > +
> > > +#define RCANFD_AFL_PAGENUM(entry)	((entry) / 16)
> (...)
> > > +#define rcar_canfd_read(priv, offset)			\
> > > +	readl(priv->base + (offset))
> > > +#define rcar_canfd_write(priv, offset, val)		\
> > > +	writel(val, priv->base + (offset))
> > > +#define rcar_canfd_set_bit(priv, reg, val)		\
> > > +	rcar_canfd_update(val, val, priv->base + (reg))
> > > +#define rcar_canfd_clear_bit(priv, reg, val)		\
> > > +	rcar_canfd_update(val, 0, priv->base + (reg))
> > > +#define rcar_canfd_update_bit(priv, reg, mask, val)	\
> > > +	rcar_canfd_update(mask, val, priv->base + (reg))
> >
> > please use static inline functions instead of defines.
> 
> OK.
> 
> >
> > > +
> > > +static void rcar_canfd_get_data(struct canfd_frame *cf,
> > > +				struct rcar_canfd_channel *priv, u32 off)
> >
> > Please use "struct rcar_canfd_channel *priv" as first argument, struct
> > canfd_frame *cf as second. Remove off, as the offset is already
> > defined by the channel.
> 
> I'll re-order priv, cf as you mentioned. I'll leave "off" arg as it is
> because it is based on FIFO number of channel + mode (CAN only or CANFD
> only). Otherwise, I will have to add another check inside this function
> for mode.
> 
> > > +{
> > > +	u32 i, lwords;
> > > +
> > > +	lwords = cf->len / sizeof(u32);
> > > +	if (cf->len % sizeof(u32))
> > > +		lwords++;
> >
> > Use DIV_ROUND_UP() instead of open coding it.
> 
> Agreed. Thanks.
> 
> >
> > > +	for (i = 0; i < lwords; i++)
> > > +		*((u32 *)cf->data + i) =
> > > +			rcar_canfd_read(priv, off + (i * sizeof(u32))); }
> > > +
> > > +static void rcar_canfd_put_data(struct canfd_frame *cf,
> > > +				struct rcar_canfd_channel *priv, u32 off)
> >
> > same here
> 
> Yes (same as _get_data)
> 
> >
> > > +{
> > > +	u32 i, j, lwords, leftover;
> > > +	u32 data = 0;
> > > +
> > > +	lwords = cf->len / sizeof(u32);
> > > +	leftover = cf->len % sizeof(u32);
> > > +	for (i = 0; i < lwords; i++)
> > > +		rcar_canfd_write(priv, off + (i * sizeof(u32)),
> > > +				 *((u32 *)cf->data + i));
> >
> > Here you don't convert the endianess...
> 
> Yes
> 
> > > +
> > > +	if (leftover) {
> > > +		u8 *p = (u8 *)((u32 *)cf->data + i);
> > > +
> > > +		for (j = 0; j < leftover; j++)
> > > +			data |= p[j] << (j * 8);
> >
> > ...here you do an implicit endianess conversion. "data" is little
> > endian, while p[j] is big endian.
> 
> Not sure I got the question correctly.
> Controller expectation of data bytes in 32bit register is bits[7:0] =
> byte0, bits[15:8] = byte1 and so on - little endian.
> For e.g. if cf->data points to byte stream H'112233445566 (cf->data[0] =
> 0x11), first rcar_canfd_write will write 0x44332211 value to register. Yes
> the host cpu is assumed little endian. In leftover case, data will be
> 0x00006655 - again little endian.
> I think I should remove this leftover logic and just mask the unused bits
> to zero as cf->data is pre-allocated for max length anyway.
> 
> p[j] is a byte?? Am I missing something?
> 
> >
> > > +		rcar_canfd_write(priv, off + (i * sizeof(u32)), data);
> > > +	}
> >
> > Have you tested to send CAN frames with len != n*4 against a different
> > controller?
> 
> Yes, with Vector VN1630A.
> 
> > > +}
> > > +
> > > +static void rcar_canfd_tx_failure_cleanup(struct net_device *ndev)
> > > +{
> > > +	u32 i;
> > > +
> > > +	for (i = 0; i < RCANFD_FIFO_DEPTH; i++)
> > > +		can_free_echo_skb(ndev, i);
> > > +}
> > > +
> (...)
> > > +static void rcar_canfd_tx_done(struct net_device *ndev) {
> > > +	struct rcar_canfd_channel *priv = netdev_priv(ndev);
> > > +	struct net_device_stats *stats = &ndev->stats;
> > > +	u32 sts;
> > > +	unsigned long flags;
> > > +	u32 ch = priv->channel;
> > > +
> > > +	do {
> >
> > You should iterare over all pending CAN frames:
> >
> > > 	for (/* nix */; (priv->tx_head - priv->tx_tail) > 0; priv-
> > >tx_tail++) {
> >
> 
> Yes, current code does iterate over pending tx'ed frames. If we use this
> for loop semantics, we may have to protect the whole loop with no real
> benefit.
> 
> >
> > > +		u8 unsent, sent;
> > > +
> > > +		sent = priv->tx_tail % RCANFD_FIFO_DEPTH;
> >
> > and check here, if that packet has really been tramsitted. Exit the
> > loop otherweise.
> 
> We are here because of tx_done and hence no need to check tx done again
> for the first iteration. Hence the do-while loop. Checks further down
> takes care of the need for more iterations/pending tx'ed frames.
> 
> >
> > > +		stats->tx_packets++;
> > > +		stats->tx_bytes += priv->tx_len[sent];
> > > +		priv->tx_len[sent] = 0;
> > > +		can_get_echo_skb(ndev, sent);
> > > +
> > > +		spin_lock_irqsave(&priv->tx_lock, flags);
> >
> > What does the tx_lock protect? The tx path is per channel, isn't it?
> 
> You are right - tx path is per channel. In tx path, head & tail are also
> used to determine when to stop/wakeup netif queue. They are incremented &
> compared in different contexts to make this decision. Per channel tx_lock
> protects this critical section.
> 
> >
> > > +		priv->tx_tail++;
> > > +		sts = rcar_canfd_read(priv,
> > > +				      RCANFD_CFSTS(ch, RCANFD_CFFIFO_IDX));
> > > +		unsent = RCANFD_CMFIFO_CFMC(sts);
> > > +
> > > +		/* Wake producer only when there is room */
> > > +		if (unsent != RCANFD_FIFO_DEPTH)
> > > +			netif_wake_queue(ndev);
> >
> > Move the netif_wake_queue() out of the loop.
> 
> With the tx logic mentioned above, I think keeping it in the loop seems
> better. For e.g. say cpu1 pumps 8 frames from an app loop and cpu0 handles
> tx_done interrupt handling: cpu1 would have stopped the queue because FIFO
> is full -> cpu0 gets tx_done interrupt and by the time it checks "unsent"
> there could be one or more frames transmitted by device (i.e.) there would
> be more space in fifo. It is better to wakeup the netif queue then and
> there so that app running on cpu1 can pump more. If we move it out of the
> loop we wake up the queue only in the end. Have I missed anything?
> 
> >
> > > +
> > > +		if (priv->tx_head - priv->tx_tail <= unsent) {
> > > +			spin_unlock_irqrestore(&priv->tx_lock, flags);
> > > +			break;
> > > +		}
> > > +		spin_unlock_irqrestore(&priv->tx_lock, flags);
> > > +
> > > +	} while (1);
> > > +
> > > +	/* Clear interrupt */
> > > +	rcar_canfd_write(priv, RCANFD_CFSTS(ch, RCANFD_CFFIFO_IDX),
> > > +			 sts & ~RCANFD_CMFIFO_CFTXIF);
> > > +	can_led_event(ndev, CAN_LED_EVENT_TX); }
> > > +
> > > +	if (cf->can_id & CAN_RTR_FLAG)
> > > +		id |= RCANFD_CMFIFO_CFRTR;
> > > +
> > > +	rcar_canfd_write(priv, RCANFD_F_CFID(ch, RCANFD_CFFIFO_IDX),
> > > +			 id);
> > > +	ptr = RCANFD_CMFIFO_CFDLC(can_len2dlc(cf->len));
> >
> > ptr usually means pointer, better call it dlc.
> 
> I used the register name "ptr". OK, will change it do dlc.
> 
> >
> > > +	rcar_canfd_write(priv, RCANFD_F_CFPTR(ch, RCANFD_CFFIFO_IDX),
> > > +			 ptr);
> > > +
> (...)
> > > +	can_put_echo_skb(skb, ndev, priv->tx_head % RCANFD_FIFO_DEPTH);
> > > +
> > > +	spin_lock_irqsave(&priv->tx_lock, flags);
> > > +	priv->tx_head++;
> > > +
> > > +	/* Start Tx: Write 0xff to CFPC to increment the CPU-side
> > > +	 * pointer for the Common FIFO
> > > +	 */
> > > +	rcar_canfd_write(priv, RCANFD_CFPCTR(ch, RCANFD_CFFIFO_IDX),
> > > +0xff);
> > > +
> > > +	/* Stop the queue if we've filled all FIFO entries */
> > > +	if (priv->tx_head - priv->tx_tail >= RCANFD_FIFO_DEPTH)
> > > +		netif_stop_queue(ndev);
> >
> > Please move the check of stop_queue, before starting the send.
> 
> OK.
> 
> >
> > > +
> > > +	spin_unlock_irqrestore(&priv->tx_lock, flags);
> > > +	return NETDEV_TX_OK;
> > > +}
> > > +
> (...)
> > > +{
> > > +	struct rcar_canfd_channel *priv =
> > > +		container_of(napi, struct rcar_canfd_channel, napi);
> > > +	int num_pkts;
> > > +	u32 sts;
> > > +	u32 ch = priv->channel;
> > > +	u32 ridx = ch + RCANFD_RFFIFO_IDX;
> > > +
> > > +	for (num_pkts = 0; num_pkts < quota; num_pkts++) {
> > > +		sts = rcar_canfd_read(priv, RCANFD_RFSTS(ridx));
> > > +		/* Clear interrupt bit */
> > > +		if (sts & RCANFD_RFFIFO_RFIF)
> > > +			rcar_canfd_write(priv, RCANFD_RFSTS(ridx),
> > > +					 sts & ~RCANFD_RFFIFO_RFIF);
> > > +
> > > +		/* Check FIFO empty condition */
> > > +		if (sts & RCANFD_RFFIFO_RFEMP)
> > > +			break;
> > > +
> > > +		rcar_canfd_rx_pkt(priv);
> >
> > This sequence looks strange. You first conditionally ack the interrupt
> > then you check for empty fifo, then read the CAN frame. I would assume
> > that you first check if there's a CAN frame, read it and then clear
> > the interrupt.
> 
> Yes, I shall re-arrange the sequence as you mentioned.
> 
> >
> > > +	}
> > > +
> > > +	/* All packets processed */
> > > +	if (num_pkts < quota) {
> > > +		napi_complete(napi);
> > > +		/* Enable Rx FIFO interrupts */
> > > +		rcar_canfd_set_bit(priv, RCANFD_RFCC(ridx),
> > RCANFD_RFFIFO_RFIE);
> (...)
> > > +	for_each_set_bit(ch, &gpriv->channels_mask, RCANFD_NUM_CHANNELS) {
> > > +		err = rcar_canfd_channel_probe(gpriv, ch);
> > > +		if (err)
> > > +			goto fail_channel;
> > > +	}
> >
> > Should the CAN IP core be clocked the whole time? What about shuting
> > down the clock and enabling it on ifup?
> 
> The fCAN clock is enabled only on ifup of one of the channels. However,
> the peripheral clock is enabled during probe to bring the controller to
> Global Operational mode. This clock cannot be turned off with the register
> values & mode retained.
> 
> > > +
> > > +	platform_set_drvdata(pdev, gpriv);
> > > +	dev_info(&pdev->dev, "global operational state (clk %d)\n",
> > > +		 gpriv->clock_select);
> (...)
> > > +	rcar_canfd_reset_controller(gpriv);
> > > +	rcar_canfd_disable_global_interrupts(gpriv);
> > > +
> > > +	for_each_set_bit(ch, &gpriv->channels_mask, RCANFD_NUM_CHANNELS) {
> > > +		priv = gpriv->ch[ch];
> > > +		if (priv) {
> >
> > This should always be true.
> 
> I agree. I thought I cleaned this up but it's in my local commits :-(
> 
> >
> > > +			rcar_canfd_disable_channel_interrupts(priv);
> > > +			unregister_candev(priv->ndev);
> > > +			netif_napi_del(&priv->napi);
> > > +			free_candev(priv->ndev);
> >
> > Please make use of rcar_canfd_channel_remove(), as you already have
> > the function.
> 
> Yes.
> 
> Thanks,
> Ramesh

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