linux-kernel - Re: [PATCH v2 2/2] phy: rockchip-emmc: use regmap_read_poll

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Message-ID: <20180110174615.GA30753@google.com>
Date:   Wed, 10 Jan 2018 09:46:26 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     Shawn Lin <shawn.lin@...k-chips.com>,
        Doug Anderson <dianders@...omium.org>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        linux-rockchip@...ts.infradead.org,
        Heiko Stuebner <heiko@...ech.de>,
        Douglas Anderson <dianders@...omium.org>,
        Ziyuan Xu <xzy.xu@...k-chips.com>,
        linux-kernel@...r.kernel.org, Caesar Wang <wxt@...k-chips.com>
Subject: Re: [PATCH v2 2/2] phy: rockchip-emmc: use regmap_read_poll_timeout
 to poll dllrdy

+ Caesar

IIUC, you didn't CC him? Also, he already sent a v2 of this patchset,
withi some minor difference.

On Wed, Jan 10, 2018 at 06:49:22PM +0800, Shawn Lin wrote:
> Just use the API instead of open-coding it, no functional change
> intended.
> 
> Signed-off-by: Shawn Lin <shawn.lin@...k-chips.com>
> Reviewed-by: Brian Norris <briannorris@...omium.org>
> Tested-by: Caesar Wang <wxt@...k-chips.com>
> Tested-by: Ziyuan Xu <xzy.xu@...k-chips.com>
> ---
> 
> Changes in v2:
> - propagate the error and print it
> - avoid using busy wait
> 
>  drivers/phy/rockchip/phy-rockchip-emmc.c | 32 +++++++++++++-------------------
>  1 file changed, 13 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/phy/rockchip/phy-rockchip-emmc.c b/drivers/phy/rockchip/phy-rockchip-emmc.c
> index 547b746..e54e78f 100644
> --- a/drivers/phy/rockchip/phy-rockchip-emmc.c
> +++ b/drivers/phy/rockchip/phy-rockchip-emmc.c
> @@ -79,6 +79,9 @@
>  #define PHYCTRL_IS_CALDONE(x) \
>  	((((x) >> PHYCTRL_CALDONE_SHIFT) & \
>  	  PHYCTRL_CALDONE_MASK) == PHYCTRL_CALDONE_DONE)
> +#define PHYCTRL_IS_DLLRDY(x) \
> +	((((x) >> PHYCTRL_DLLRDY_SHIFT) & \
> +	  PHYCTRL_DLLRDY_MASK) == PHYCTRL_DLLRDY_DONE)
>  
>  struct rockchip_emmc_phy {
>  	unsigned int	reg_offset;
> @@ -93,7 +96,6 @@ static int rockchip_emmc_phy_power(struct phy *phy, bool on_off)
>  	unsigned int dllrdy;
>  	unsigned int freqsel = PHYCTRL_FREQSEL_200M;
>  	unsigned long rate;
> -	unsigned long timeout;
>  	int ret;
>  
>  	/*
> @@ -217,28 +219,20 @@ static int rockchip_emmc_phy_power(struct phy *phy, bool on_off)

I'd probably like Doug's comment on the comment rewording (and
functional change) since he wrote them in the first place, but this is
also where you and Caesar differed. Caesar just deleted most of the last
paragraph, because it really applied just to the busy wait loop, not
really to the sleep-based loop that you're putting in here.

>  	 * 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:
> +	 * generous and give it 50ms.  We still 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
> +	 *   be a power or performance problem to wait.  We expect it

Why would it be a power problem to just "wait"? (Hint: it was only a
potential power problem to *busy* wait, where we're spinning in a tight
loop.)

>  	 *   only at boot / resume.  In both cases, eMMC is probably on the
> -	 *   critical path so busy waiting a little extra time should be OK.
> +	 *   critical path so waiting a little extra time should be OK.

If we all agree that the above *performance* reasoning is not important,
then it should be fine to do the conversion to the sleep/polling macro,
and I think the best comment is just to delete all the above about power
and performance of this wait loop. It was only necessary to justify the
udelay() loop.

So IOW, I think Caesar's version was better :)

Otherwise, my 'Reviewed-by' for both series stands.

Doug, do you have any thoughts? Or at least Caesar and Shawn: please
choose one of your patch series, not both!

Brian

>  	 */
> -	timeout = jiffies + msecs_to_jiffies(50);
> -	do {
> -		udelay(1);
> -
> -		regmap_read(rk_phy->reg_base,
> -			rk_phy->reg_offset + GRF_EMMCPHY_STATUS,
> -			&dllrdy);
> -		dllrdy = (dllrdy >> PHYCTRL_DLLRDY_SHIFT) & PHYCTRL_DLLRDY_MASK;
> -		if (dllrdy == PHYCTRL_DLLRDY_DONE)
> -			break;
> -	} while (!time_after(jiffies, timeout));
> -
> -	if (dllrdy != PHYCTRL_DLLRDY_DONE) {
> -		pr_err("rockchip_emmc_phy_power: dllrdy timeout.\n");
> -		return -ETIMEDOUT;
> +	ret = regmap_read_poll_timeout(rk_phy->reg_base,
> +				       rk_phy->reg_offset + GRF_EMMCPHY_STATUS,
> +				       dllrdy, PHYCTRL_IS_DLLRDY(dllrdy),
> +				       1, 50 * USEC_PER_MSEC);
> +	if (ret) {
> +		pr_err("%s: dllrdy failed %d.\n", __func__, ret);
> +		return ret;
>  	}
>  
>  	return 0;
> -- 
> 1.9.1
> 
>