netdev - Re: [PATCH 05/10] smc91x: prepare for SMC_IO_SHIFT to be a platform configurable variable

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Date:	Thu, 26 Jun 2008 20:00:34 -0400 (EDT)
From:	Nicolas Pitre <nico@....org>
To:	Eric Miao <eric.y.miao@...il.com>
Cc:	linux-arm-kernel <linux-arm-kernel@...ts.arm.linux.org.uk>,
	linux-netdev <netdev@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Eric Miao <eric.miao@...vell.com>
Subject: Re: [PATCH 05/10] smc91x: prepare for SMC_IO_SHIFT to be a platform
 configurable variable

On Tue, 24 Jun 2008, Eric Miao wrote:

> From: Eric Miao <eric.miao@...vell.com>
> 
> Now one can use the following code
> 
>   #define SMC_IO_SHIFT	smc_io_shift
> 
> to make SMC_IO_SHIFT a variable. This, however, will slightly increase
> the CPU overhead and have negative impact on the network performance.

Actually I think you should store the io shift variable in the smc_local 
structure rather than using a global, and make that define be this 
instead:

   #define SMC_IO_SHIFT        lp->io_shift

This would allow multiple instances with different values of io shift at 
the same time (if ever such a config happens), and be slightly more 
efficient on ARM too.

> The tradeoff is, this can be specified in the smc91x platform data so
> that multiple boards support can be built in a single zImage.
> 
> Signed-off-by: Eric Miao <eric.miao@...vell.com>

With the above change:

Acked-by: Nicolas Pitre <nico@....org>

> ---
>  drivers/net/smc91x.c   |    7 +++++--
>  include/linux/smc91x.h |    7 +++++++
>  2 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/smc91x.c b/drivers/net/smc91x.c
> index caa0308..3a319f2 100644
> --- a/drivers/net/smc91x.c
> +++ b/drivers/net/smc91x.c
> @@ -105,6 +105,8 @@ MODULE_PARM_DESC(watchdog, "transmit timeout in milliseconds");
>  MODULE_LICENSE("GPL");
>  MODULE_ALIAS("platform:smc91x");
>  
> +static int smc_io_shift __maybe_unused;
> +
>  /*
>   * The internal workings of the driver.  If you are changing anything
>   * here with the SMC stuff, you should have the datasheet and know
> @@ -2136,9 +2138,10 @@ static int smc_drv_probe(struct platform_device *pdev)
>  
>  	lp = netdev_priv(ndev);
>  
> -	if (pd)
> +	if (pd) {
>  		memcpy(&lp->cfg, pd, sizeof(lp->cfg));
> -	else {
> +		smc_io_shift = SMC91X_IO_SHIFT(lp->cfg.flags);
> +	} else {
>  		lp->cfg.flags |= (SMC_CAN_USE_8BIT)  ? SMC91X_USE_8BIT  : 0;
>  		lp->cfg.flags |= (SMC_CAN_USE_16BIT) ? SMC91X_USE_16BIT : 0;
>  		lp->cfg.flags |= (SMC_CAN_USE_32BIT) ? SMC91X_USE_32BIT : 0;
> diff --git a/include/linux/smc91x.h b/include/linux/smc91x.h
> index 90434db..0dea945 100644
> --- a/include/linux/smc91x.h
> +++ b/include/linux/smc91x.h
> @@ -7,6 +7,13 @@
>  
>  #define SMC91X_NOWAIT		(1 << 3)
>  
> +/* two bits for IO_SHIFT, let's hope later designs will keep this sane */
> +#define SMC91X_IO_SHIFT_0	(0 << 4)
> +#define SMC91X_IO_SHIFT_1	(1 << 4)
> +#define SMC91X_IO_SHIFT_2	(2 << 4)
> +#define SMC91X_IO_SHIFT_3	(3 << 4)
> +#define SMC91X_IO_SHIFT(x)	(((x) >> 4) & 0x3)
> +
>  struct smc91x_platdata {
>  	unsigned long flags;
>  };
> -- 
> 1.5.4.3
> 


Nicolas
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