[PATCH] [RFC] fec: fix calculation of mii bus speed on mxs

[Sascha Hauer]

Hi Uwe,

On Thu, Sep 06, 2012 at 03:50:01PM +0200, Uwe Kleine-König wrote:
> According to a comment in Linux' fec driver, i.MX28 uses the same
> formula for determination of the frequency divider as i.MX6, that is
> (different from the i.MX28 manual):
> 
> 	parent clock / ((MII_SPEED + 1) * 2)
> 
> instead of
> 
> 	parent clock / (MII_SPEED * 2)
> 
> on the older i.MX SoCs. Fix the calculation accordingly.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
> --
> But note that this doesn't fix accessing the phy on my machine. The
> calculated value is 9 (with and without this patch btw) but accessing
> the phy only gets reliable with a value of >=20 or alternatively don't
> set the SPEED value before reading and writing a mii register but only
> on probe.
> 
> The Freescale kernel 2.6.35_10.12.01 does the following instead (in
> fec_switch.c):
> 
> 	fep->phy_speed = DIV_ROUND_UP(clk_get_rate(fep->clk), 5000000) << 1;
> #ifdef CONFIG_ARCH_MXS
> 	/* Can't get phy(8720) ID when set to 2.5M on MX28, lower it */
> 	fep->phy_speed <<= 2;
> #endif
> 
> which would result in 40 (and is unaware of the changed formula).
> 
> I didn't have an opportunity to check the signals with an oszilloscope, but
> intend to fetch that later.
> ---
>  drivers/net/fec_imx.c |   48 ++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 38 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/net/fec_imx.c b/drivers/net/fec_imx.c
> index 599a9b4..969c903 100644
> --- a/drivers/net/fec_imx.c
> +++ b/drivers/net/fec_imx.c
> @@ -47,6 +47,41 @@ struct fec_frame {
>  	uint8_t head[16];	/* MAC header(6 + 6 + 2) + 2(aligned) */
>  };
>  
> +static void fec_miidev_setspeed(struct fec_priv *fec)
> +{
> +	u32 mii_speed;
> +
> +	mii_speed = DIV_ROUND_UP(imx_get_fecclk(), 5000000);
> +
> +#ifdef CONFIG_ARCH_MXS
> +	/*
> +	 * Compared to the other imx socs imx28 and imx6 have an additional "+1"
> +	 * in the formula for MII_SPEED. In MCIMX28RM Rev.1, 2010 this is not
> +	 * documented though.
> +	 */
> +	mii_speed -= 1;
> +#endif

Please use a if (cpu_is_mx28()) instead. While we are at it we should
also do this for i.MX6 and add a cpu_is_mx6() aswell.

Sascha

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