[PATCH 05/04] *** NOT FOR RELEASE *** HACK *** Work around MII clock issue ***

[John Rigby]

I think the fec's parent clock is the ipb clock not the ppc core clock.
Could that be the problem?

On Wed, May 6, 2009 at 2:21 PM, Wolfgang Denk <wd at denx.de> wrote:

> Signed-off-by: Wolfgang Denk <wd at denx.de>
> Cc: Grant Likely <grant.likely at secretlab.ca>
> Cc: John Rigby <jcrigby at gmail.com>
> ---
> This patch is NOT intended for inclusion into mainline, but rather a
> request for help. For some reason which I don't understand yet, the
> Ethernet interface on the ARIA board does not work in the default
> configuration, because MII probing fails.
>
> What I'm seeing is this; the problem is with this part of code in
> "drivers/net/fs_enet/mii-fec.c":
>
> 156         fec->mii_speed = ((ppc_proc_freq + 4999999) / 5000000) << 1;
> ...
> 163         out_be32(&fec->fecp->fec_mii_speed, fec->mii_speed);
>
> I added some debug messages, and this is what I see:
>
> On the ADS5121, we have the CPU clocked at 400 MHz.  I get:
> ...
> ## ppc_proc_freq = 399999996, fec->mii_speed = 160
> FEC MII Bus: probed
> ...
> It works fine.
>
> According to the Ref. Man.:
>        A value of 0 in this field turns off the MDC and leaves it in
>        a low-voltage state. Any non-zero value results in the MDC
>        frequency of 1/(mii_speed*2) of the system clock frequency.
> that means we have a MDC frequency of
>        400 MHz / (2 * 160) = 1.25 MHz
> which is obviously within the 2.5 MHz limit.
>
> Now ARIA is currently running at 316.8 MHz, and this is what I get:
> ...
> ## ppc_proc_freq = 316800000, fec->mii_speed = 128
> fsl-fec-mdio: probe of 80002800.mdio failed with error -5
> ...
> It fails. MDC frequency is
>        316.8 MHz / (2 * 128) = 1.24 MHz
> which should be fine.
>
> However, If I change the code to
>
> fec->mii_speed = (((ppc_proc_freq / 1000000) / 30) + 1) << 1;
>
> then I get:
> ...
> ## ppc_proc_freq = 316800000, fec->mii_speed = 22
> FEC MII Bus: probed
> ... and it's working!!! However, I compute MDC frequency as
>        316.8 MHz / (2 * 22) = 7.2 MHz
> which is far above the maximum allowed clock of 2.5 MHz ???
>
> Has anybody any idea what might be going on here?
>
>
>  drivers/net/fs_enet/mii-fec.c |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/net/fs_enet/mii-fec.c b/drivers/net/fs_enet/mii-fec.c
> index 9d8bd97..a51dd83 100644
> --- a/drivers/net/fs_enet/mii-fec.c
> +++ b/drivers/net/fs_enet/mii-fec.c
> @@ -153,8 +153,12 @@ static int __devinit fs_enet_mdio_probe(struct
> of_device *ofdev,
>        if (!fec->fecp)
>                goto out_fec;
>
> +#if 0
>        fec->mii_speed = ((ppc_proc_freq + 4999999) / 5000000) << 1;
> -
> +#else
> +       fec->mii_speed = (((ppc_proc_freq / 1000000) / 30) + 1) << 1;
> +       printk("## ppc_proc_freq = %d, fec->mii_speed = %d\n",
> ppc_proc_freq, fec->mii_speed);
> +#endif
>        setbits32(&fec->fecp->fec_r_cntrl, FEC_RCNTRL_MII_MODE);
>        setbits32(&fec->fecp->fec_ecntrl, FEC_ECNTRL_PINMUX |
>                                          FEC_ECNTRL_ETHER_EN);
> --
> 1.6.0.6
>
>
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