linux-kernel - Re: [PATCH v2] mmc: dw_mmc: Disable low power mode if SDIO interrupts are used

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Date:	Tue, 24 Jul 2012 10:36:52 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	linux-mmc@...r.kernel.org, Chris Ball <cjb@...top.org>,
	Will Newton <will.newton@...tec.com>,
	James Hogan <james.hogan@...tec.com>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	linux-kernel@...r.kernel.org,
	Grant Grundler <grundler@...omium.org>,
	Olof Johansson <olofj@...omium.org>,
	shashidharh@...avyalabs.com, ki0351.kim@...sung.com
Subject: Re: [PATCH v2] mmc: dw_mmc: Disable low power mode if SDIO interrupts
 are used

On 07/24/2012 02:02 AM, Doug Anderson wrote:
> The documentation for the dw_mmc part says that the low power
> mode should normally only be set for MMC and SD memory and should
> be turned off for SDIO cards that need interrupts detected.
> 
> The best place I could find to do this is when the SDIO interrupt
> was first enabled.  I rely on the fact that dw_mci_setup_bus()
> will be called when it's time to reenable.
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
> Changes in v2:
> - Commenting fixes requested by Grant Grundler.
> - Be extra certain that we don't re-turn on the low power mode in
>   CLKENA in dw_mci_setup_bus() if SDIO interrupts are enabled.
>   There are no known instances of this happening but it's good to be safe.
> 
>  drivers/mmc/host/dw_mmc.c |   43 ++++++++++++++++++++++++++++++++++++++++---
>  1 files changed, 40 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index 72dc3cd..0ab1771 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -627,6 +627,7 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot)
>  {
>  	struct dw_mci *host = slot->host;
>  	u32 div;
> +	u32 clk_en_a;
>  
>  	if (slot->clock != host->current_speed) {
>  		div = host->bus_hz / slot->clock;
> @@ -659,9 +660,11 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot)
>  		mci_send_cmd(slot,
>  			     SDMMC_CMD_UPD_CLK | SDMMC_CMD_PRV_DAT_WAIT, 0);
>  
> -		/* enable clock */
> -		mci_writel(host, CLKENA, ((SDMMC_CLKEN_ENABLE |
> -			   SDMMC_CLKEN_LOW_PWR) << slot->id));
> +		/* enable clock; only low power if no SDIO */
> +		clk_en_a = SDMMC_CLKEN_ENABLE << slot->id;
> +		if (!(mci_readl(host, INTMASK) & SDMMC_INT_SDIO(slot->id)))
> +			clk_en_a |= SDMMC_CLKEN_LOW_PWR << slot->id;
> +		mci_writel(host, CLKENA, clk_en_a);
>  
>  		/* inform CIU */
>  		mci_send_cmd(slot,
> @@ -862,6 +865,32 @@ static int dw_mci_get_cd(struct mmc_host *mmc)
>  	return present;
>  }
>  
> +/*
> + * Disable lower power mode.
> + *
> + * Low power mode will stop the card clock when idle.  According to
> + * documentation (Exynos 5250 User's Manual 0.04, description of
> + * CLKENA register) we should disable low power mode for SDIO cards
> + * if we need interrupts to work.
> + *
As Seungwon is mentioned, that is not exynos5250 specific.
> + * This function is fast if the power mode is already disabled.
> + */
> +static void dw_mci_disable_low_power(struct mmc_host *mmc)
> +{
> +	struct dw_mci_slot *slot = mmc_priv(mmc);
> +	struct dw_mci *host = slot->host;
> +	u32 clk_en_a;
> +	const u32 clken_low_pwr = SDMMC_CLKEN_LOW_PWR << slot->id;
> +
> +	clk_en_a = mci_readl(host, CLKENA);
> +
> +	if (clk_en_a & clken_low_pwr) {
> +		mci_writel(host, CLKENA, clk_en_a & ~clken_low_pwr);
> +		mci_send_cmd(slot, SDMMC_CMD_UPD_CLK |
> +			     SDMMC_CMD_PRV_DAT_WAIT, 0);
> +	}
> +}
> +
>  static void dw_mci_enable_sdio_irq(struct mmc_host *mmc, int enb)
>  {
>  	struct dw_mci_slot *slot = mmc_priv(mmc);
> @@ -871,6 +900,14 @@ static void dw_mci_enable_sdio_irq(struct mmc_host *mmc, int enb)
>  	/* Enable/disable Slot Specific SDIO interrupt */
>  	int_mask = mci_readl(host, INTMASK);
>  	if (enb) {
> +		/*
> +		 * Turn off low power mode if it was enabled.  This is a bit of
> +		 * a heavy operation and we disable / enable IRQs a lot, so
> +		 * we'll leave low power mode disabled and it will get
> +		 * re-enabled again in dw_mci_setup_bus().
> +		 */
> +		dw_mci_disable_low_power(mmc);
How about using "slot" instead of "mmc"?
> +
>  		mci_writel(host, INTMASK,
>  			   (int_mask | SDMMC_INT_SDIO(slot->id)));
>  	} else {
> 


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