Subject: Re: [PATCH v5] can: add Renesas R-Car CAN driver

From: Marc Kleine-Budde <[email-masked]>
Date: Thu, 13 Feb 2014 13:12:53 +0100

On 01/25/2014 02:34 AM, Sergei Shtylyov wrote:
> Hello.
> 
> On 01/20/2014 12:18 PM, Marc Kleine-Budde wrote:
> 
>>> Add support for the CAN controller found in Renesas R-Car SoCs.
> 
>>> Signed-off-by: Sergei Shtylyov <[email-masked]>
> 
>>> ---
>>> The patch is against the 'linux-can-next.git' repo.
> 
> [...]
>>> Index: linux-can-next/drivers/net/can/rcar_can.c
>>> ===================================================================
>>> --- /dev/null
>>> +++ linux-can-next/drivers/net/can/rcar_can.c
>>> @@ -0,0 +1,857 @@
> [...]
>>> +/* Mailbox registers structure */
>>> +struct rcar_can_mbox_regs {
>>> +    u32 id;        /* IDE and RTR bits, SID and EID */
>>> +    u8 stub;    /* Not used */
>>> +    u8 dlc;        /* Data Length Code - bits [0..3] */
>>> +    u8 data[8];    /* Data Bytes */
>>> +    u8 tsh;        /* Time Stamp Higher Byte */
>>> +    u8 tsl;        /* Time Stamp Lower Byte */
>>> +} __packed;
> 
>> If you have contact to the hardware designer please blame him for
> 
>    Unfortunately, we don't.
> 
>> placing the data register unaligned into the register space. :)
> 
>    It's not even the only one or worst example of questionable register
> design in this module IMO.
> 
> [...]
>>> +static void rcar_can_tx_done(struct net_device *ndev)
>>> +{
>>> +    struct rcar_can_priv *priv = netdev_priv(ndev);
>>> +    struct net_device_stats *stats = &ndev->stats;
>>> +    int i;
>>> +
>>> +    spin_lock(&priv->skb_lock);
>>> +    for (i = 0; i < priv->frames_queued; i++)
>>> +        can_get_echo_skb(ndev, i);
>>> +    stats->tx_bytes += priv->bytes_queued;
>>> +    stats->tx_packets += priv->frames_queued;
>>> +    priv->bytes_queued = 0;
>>> +    priv->frames_queued = 0;
>>> +    spin_unlock(&priv->skb_lock);
> 
>> This looks broken. What happens if you send 2 CAN frames in a row, the
>> first one is send, a TX complete interrupt is issued and you handle it
>> here? You assume, that all CAN frames have been sent.
> 
>    TX interrupt will be issued only when TX FIFO gets empty (all 2 frames
> have been transmitted in this case). Please see the comment to the
> RCAR_CAN_MIER1_TXFIT bit.

Does the hardware have a TX complete interrupt? If you only have TX FIFO
empty, you have to limit the FIFO depth to 1.

>>> +static irqreturn_t rcar_can_interrupt(int irq, void *dev_id)
>>> +{
>>> +    struct net_device *ndev = (struct net_device *)dev_id;
> 
>> the cast is not needed
> 
>    Removed.
> 
> [...]
>>> +static void rcar_can_set_bittiming(struct net_device *dev)
>>> +{
>>> +    struct rcar_can_priv *priv = netdev_priv(dev);
>>> +    struct can_bittiming *bt = &priv->can.bittiming;
>>> +    u32 bcr;
>>> +    u8 clkr;
>>> +
>>> +    /* Don't overwrite CLKR with 32-bit BCR access */
>>> +    /* CLKR has 8-bit access */
> 
>> Can you explain the register layout here? Why do you access BCR with 32
>> bits when the register is defined as 3x8 bit? Can't you make it a
>> standard 32 bit register?
> 
> 1. According to documentation BCR is the 24-bit register.
> Actually we can consider some 32-bit register that combines BCR and
> CLKR but according to documentation there are two separate registers.
> 2. BCR has 8- ,16-, and 32-bit access (according to documentation).
> 3. This is the algorithm that the documentation suggests.
> 4. We had a driver version with byte access but 32-bit access seems
> shorter.

Please use a normal read-modify-write 32 bit access.

Marc

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