netdev - Re: [PATCH 3/4] net/fec: set phy_speed to the optimal frequency 2.5 MHz

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Message-ID: <4E77C4A2.1060802@boundarydevices.com>
Date:	Mon, 19 Sep 2011 15:39:30 -0700
From:	Troy Kisky <troy.kisky@...ndarydevices.com>
To:	Shawn Guo <shawn.guo@...aro.org>
CC:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	linux-arm-kernel@...ts.infradead.org, patches@...aro.org
Subject: Re: [PATCH 3/4] net/fec: set phy_speed to the optimal frequency 2.5
 MHz

On 9/18/2011 4:54 AM, Shawn Guo wrote:
> With the unnecessary 1 bit left-shift on fep->phy_speed during the
> calculation, the phy_speed always runs at the half frequency of the
> optimal one 2.5 MHz.
>
> The patch removes that 1 bit left-shift to get the optimal phy_speed.
>
> Signed-off-by: Shawn Guo<shawn.guo@...aro.org>
> ---
>   drivers/net/fec.c |    2 +-
>   1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/net/fec.c b/drivers/net/fec.c
> index 5ef0e34..04206e4 100644
> --- a/drivers/net/fec.c
> +++ b/drivers/net/fec.c
> @@ -1007,7 +1007,7 @@ static int fec_enet_mii_init(struct platform_device *pdev)
>   	/*
>   	 * Set MII speed to 2.5 MHz (= clk_get_rate() / 2 * phy_speed)
>   	 */
> -	fep->phy_speed = DIV_ROUND_UP(clk_get_rate(fep->clk), 5000000)<<  1;
> +	fep->phy_speed = DIV_ROUND_UP(clk_get_rate(fep->clk), 5000000);
>   	writel(fep->phy_speed, fep->hwp + FEC_MII_SPEED);
>
>   	fep->mii_bus = mdiobus_alloc();
Do you need to round up to an even value? Is the hardware documentation 
wrong?
Does this need a quirk? What boards has this been verified to fix?

Thanks
Troy

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