Subject: Re: [PATCH 4/6] rionet: add memory access to simulated Ethernet over rapidio

From: Andrew Morton <[email-masked]>
Date: Tue, 12 May 2009 15:10:29 -0700

On Tue, 12 May 2009 16:36:01 +0800
Li Yang <[email-masked]> wrote:

> Through the newly added IO memory access of RapidIO, sender can
> write directly to recipient's rx buffer, either by cpu or DMA engine.
>
> ...
>
> +/* Definitions for rionet memory map driver */
> +#define RIONET_DRVID		0x101
> +#define RIONET_MAX_SK_DATA_SIZE	0x1000
> +#define RIONET_MEM_RIO_BASE	0x10000000
> +#define RIONET_TX_RX_BUFF_SIZE	(0x1000 * (128 + 128))
> +#define RIONET_QUEUE_NEXT(x)	(((x) < 127) ? ((x) + 1) : 0)

References its arg multiple times, hence is buggy or inefficient when
passed an expression with side-effects.

	static inline int rionet_queue_next(int x)

would be better.  Assuming that some sane identifier is used instead of
"x".

> +#define RIONET_QUEUE_INC(x)	(x = RIONET_QUEUE_NEXT(x))

It's pretty ugly to hide an assignment inside a macro like this.  Why
not do

	foo = rionet_queue_inc(foo);

at the callsites?  It makes it much clearer for the reader.

>
> ...
>
> +#ifdef CONFIG_RIONET_MEMMAP
> +static int rio_send_mem(struct sk_buff *skb,
> +				struct net_device *ndev, struct rio_dev *rdev)
> +{
> +	struct rionet_private *rnet = netdev_priv(ndev);
> +	int enqueue, dequeue;
> +
> +	if (!rdev)
> +		return -EFAULT;

Is that an appropriate error code?

> ...