linux-kernel - Re: [PATCH] mfd: RK808: Add register caching

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Date:	Thu, 11 Sep 2014 11:39:23 +0800
From:	Chris Zhong <zyw@...k-chips.com>
To:	Doug Anderson <dianders@...omium.org>,
	Lee Jones <lee.jones@...aro.org>,
	Heiko Stuebner <heiko@...ech.de>
CC:	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org,
	Sonny Rao <sonnyrao@...omium.org>, sameo@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mfd: RK808: Add register caching


On 09/10/2014 07:06 AM, Doug Anderson wrote:
> Let's define the voltatile registers (those that can't be cached) and
> enable caching.  The rk808 is accessed almost constantly with cpufreq
> so this is really nice.
>
> As measured by ftrace:
>    before this change: cpu0_set_target() => ~2200us
>    after this change:  cpu0_set_target() =>  ~500us
>
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
>   drivers/mfd/rk808.c | 30 ++++++++++++++++++++++++++++++
>   1 file changed, 30 insertions(+)
>
> diff --git a/drivers/mfd/rk808.c b/drivers/mfd/rk808.c
> index 0324422..bd02150 100644
> --- a/drivers/mfd/rk808.c
> +++ b/drivers/mfd/rk808.c
> @@ -29,10 +29,40 @@ struct rk808_reg_data {
>   	int value;
>   };
>   
> +static bool rk808_is_volatile_reg(struct device *dev, unsigned int reg)
> +{
> +	/*
> +	 * Notes:
> +	 * - Technically the ROUND_30s bit makes RTC_CTRL_REG volatile, but
> +	 *   we don't use that feature.  It's better to cache.
> +	 * - It's unlikely we care that RK808_DEVCTRL_REG is volatile since
> +	 *   bits are cleared in case when we shutoff anyway, but better safe.
> +	 */
> +
> +	switch (reg) {
> +	case RK808_SECONDS_REG ... RK808_WEEKS_REG:
> +	case RK808_RTC_STATUS_REG:
> +	case RK808_VB_MON_REG:
> +	case RK808_THERMAL_REG:
> +	case RK808_DCDC_UV_STS_REG:
> +	case RK808_LDO_UV_STS_REG:
> +	case RK808_DCDC_PG_REG:
> +	case RK808_LDO_PG_REG:
> +	case RK808_DEVCTRL_REG:
> +	case RK808_INT_STS_REG1:
> +	case RK808_INT_STS_REG2:
> +		return true;
> +	}
> +
> +	return false;
> +}
> +
>   static const struct regmap_config rk808_regmap_config = {
>   	.reg_bits = 8,
>   	.val_bits = 8,
>   	.max_register = RK808_IO_POL_REG,
> +	.cache_type = REGCACHE_RBTREE,
> +	.volatile_reg = rk808_is_volatile_reg,
>   };
>   
>   static struct resource rtc_resources[] = {
Reviewed-by: Chris Zhong <zyw@...k-chips.com>
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