Subject: Re: [PATCH net-next v2 2/4] can: cc770: add legacy ISA bus driver for the CC770 and AN82527

From: Marc Kleine-Budde <[email-masked]>
Date: Tue, 10 Jan 2012 00:11:29 +0100

On 01/09/2012 10:47 PM, Wolfgang Zarre wrote:
[...]

>>> OK. My concern: Can we be sure that 16bit accesses are always
>> supported
>>> by the hardware? Does a spinlock_irqsave/spinlock_irqrestore around
>> the
>>> 8bit accesses already help?
>>
>> Hmmm... are there any register reads that need the
>> same 'double cycle' sequence ??
>> If so you need to stop reads being interleaved (with
>> themselves and writes) so requesting a 16bit access
>> doesn't help.
>>
>> Which means you need a spinlock...
>>
>>     David
>>
>>
> 
> @David: Thank You very much for that hint. You are right and to
> implement correct we need a spinlock.
> 
> @Wolfgang: I was thinking about Your question regarding 8/16 bit and
> in fact it wouldn't work at all on a clean 8 bit cards.
> 
> Further it wouldn't work on 16 bit cards where the MSB is not equal
> to base port +1 and anyway, it's depending always on how the chip is
> interfaced to the ISA bus and in which mode the chip is configured.
> 
> 
> And therefore I was giving David's hint a try in using a spinlock in
> function cc770_isa_port_write_reg_indirect() and patched as follows:
> 
> ---------------------------------------------------------------------
> diff --git a/drivers/net/can/cc770/cc770.c b/drivers/net/can/cc770/cc770.c
> index 2d12f89..dad6707 100644
> --- a/drivers/net/can/cc770/cc770.c
> +++ b/drivers/net/can/cc770/cc770.c
> @@ -460,15 +460,6 @@ static netdev_tx_t cc770_start_xmit(struct sk_buff
> *skb, struct net_device *dev)
> 
>      stats->tx_bytes += dlc;
> 
> -
> -    /*
> -     * HM: We had some cases of repeated IRQs so make sure the
> -     * INT is acknowledged I know it's already further up, but
> -     * doing again fixed the issue
> -     */
> -    cc770_write_reg(priv, msgobj[mo].ctrl0,
> -            MSGVAL_UNC | TXIE_UNC | RXIE_UNC | INTPND_RES);
> -
>      return NETDEV_TX_OK;
>  }
> 
> @@ -689,12 +680,6 @@ static void cc770_tx_interrupt(struct net_device
> *dev, unsigned int o)
>      /* Nothing more to send, switch off interrupts */
>      cc770_write_reg(priv, msgobj[mo].ctrl0,
>              MSGVAL_RES | TXIE_RES | RXIE_RES | INTPND_RES);
> -    /*
> -     * We had some cases of repeated IRQ so make sure the
> -     * INT is acknowledged
> -     */
> -    cc770_write_reg(priv, msgobj[mo].ctrl0,
> -            MSGVAL_UNC | TXIE_UNC | RXIE_UNC | INTPND_RES);
> 
>      stats->tx_packets++;
>      can_get_echo_skb(dev, 0);
> diff --git a/drivers/net/can/cc770/cc770_isa.c
> b/drivers/net/can/cc770/cc770_isa.c
> index 4be5fe2..fe39eed 100644
> --- a/drivers/net/can/cc770/cc770_isa.c
> +++ b/drivers/net/can/cc770/cc770_isa.c
> @@ -110,6 +110,9 @@ MODULE_PARM_DESC(bcr, "Bus configuration register
> (default=0x40 [CBY])");
>  #define CC770_IOSIZE          0x20
>  #define CC770_IOSIZE_INDIRECT 0x02
> 
> +/* Spinlock for cc770_isa_port_write_reg_indirect */
> +static DEFINE_SPINLOCK( outb_lock);
> +

Do we need a global or a per device spin lock? If this should be a per
device one, please introduce a cc770_isa_priv and put the spinlock
there. Don't forget to initialize the spinlock.

>  static struct platform_device *cc770_isa_devs[MAXDEV];
> 
>  static u8 cc770_isa_mem_read_reg(const struct cc770_priv *priv, int reg)
> @@ -147,9 +150,12 @@ static void cc770_isa_port_write_reg_indirect(const
> struct cc770_priv *priv,
>                          int reg, u8 val)
>  {
>      unsigned long base = (unsigned long)priv->reg_base;
> +    unsigned long flags;

please indent with tab, not space (your mailer probably converts tabs to
space)

> 
> +    spin_lock_irqsave( &outb_lock, flags);
                         ^

please remove the whitespace.

>      outb(reg, base);
>      outb(val, base + 1);
> +    spin_unlock_irqrestore( &outb_lock, flags);   
                              ^                   ^^^
please remove this and trailing whitespace.

>  }
> 
>  static int __devinit cc770_isa_probe(struct platform_device *pdev)
> ----------------------------------------------------------------------

cheers, Marc

-- 
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