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

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Message-id: <004d01cd693a$0a55d7b0$1f018710$%jun@samsung.com>
Date:	Tue, 24 Jul 2012 10:17:06 +0900
From:	Seungwon Jeon <tgih.jun@...sung.com>
To:	'Doug Anderson' <dianders@...omium.org>, linux-mmc@...r.kernel.org
Cc:	'Chris Ball' <cjb@...top.org>,
	'Will Newton' <will.newton@...tec.com>,
	'James Hogan' <james.hogan@...tec.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

July 24, 2012, Doug Anderson <dianders@...omium.org> 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);
I have followed this patch from v1.
I think it's a good point.
Looks good to me.

> 
>  		/* 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.
Above comment is correct, but this is not specific for Exynos5250.
Exynos5250 is just one of host controllers base on Synopsys's.
It'd be better to remove the part related to Exynos you mentioned .


> + *
> + * This function is fast if the power mode is already disabled.
Definitely, low power mode not power mode, right?

Best regards,
Seungwon Jeon

> + */
> +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);
> +
>  		mci_writel(host, INTMASK,
>  			   (int_mask | SDMMC_INT_SDIO(slot->id)));
>  	} else {
> --
> 1.7.7.3
> 
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