linux-kernel - Re: [PATCH 3/3] phy: rockchip-emmc: Wait even longer for the DLL to lock

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Message-ID: <5773D227.6010502@ti.com>
Date:	Wed, 29 Jun 2016 19:20:31 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Douglas Anderson <dianders@...omium.org>,
	Heiko Stuebner <heiko@...ech.de>, <ulf.hansson@...aro.org>
CC:	<shawn.lin@...k-chips.com>, <linux-rockchip@...ts.infradead.org>,
	<linux-mmc@...r.kernel.org>, <briannorris@...omium.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] phy: rockchip-emmc: Wait even longer for the DLL to
 lock



On Monday 27 June 2016 11:09 PM, Douglas Anderson wrote:
> Two times out of 2000 reboots I ran into the error message
> "rockchip_emmc_phy_power: dllrdy timeout".  Presumably there is some
> corner case where the DLL just takes a little longer to timeout.  Let's
> give it even more time to handle these corner cases.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

Acked-by: Kishon Vijay Abraham I <kishon@...com>
> ---
>  drivers/phy/phy-rockchip-emmc.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/phy/phy-rockchip-emmc.c b/drivers/phy/phy-rockchip-emmc.c
> index a2aa6aca7dec..fd57345ffed2 100644
> --- a/drivers/phy/phy-rockchip-emmc.c
> +++ b/drivers/phy/phy-rockchip-emmc.c
> @@ -206,8 +206,18 @@ static int rockchip_emmc_phy_power(struct phy *phy, bool on_off)
>  	 * per the math: 10.2 us * (50000000 Hz / 100000 Hz) => 5.1 ms
>  	 * Hopefully we won't be running at 100 kHz, but we should still make
>  	 * sure we wait long enough.
> +	 *
> +	 * NOTE: There appear to be corner cases where the DLL seems to take
> +	 * extra long to lock for reasons that aren't understood.  In some
> +	 * extreme cases we've seen it take up to over 10ms (!).  We'll be
> +	 * generous and give it 50ms.  We still busy wait here because:
> +	 * - In most cases it should be super fast.
> +	 * - This is not called lots during normal operation so it shouldn't
> +	 *   be a power or performance problem to busy wait.  We expect it
> +	 *   only at boot / resume.  In both cases, eMMC is probably on the
> +	 *   critical path so busy waiting a little extra time should be OK.
>  	 */
> -	timeout = jiffies + msecs_to_jiffies(10);
> +	timeout = jiffies + msecs_to_jiffies(50);
>  	do {
>  		udelay(1);
>  
>