linux-kernel - Re: [PATCH v4] mmc: dw_mmc: Disable low power mode if SDIO interrupts are used

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Date:	Tue, 07 Aug 2012 23:40:59 -0400
From:	Chris Ball <cjb@...top.org>
To:	Seungwon Jeon <tgih.jun@...sung.com>
Cc:	'Doug Anderson' <dianders@...omium.org>, linux-mmc@...r.kernel.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 v4] mmc: dw_mmc: Disable low power mode if SDIO interrupts are used

Hi,

On Thu, Jul 26 2012, Seungwon Jeon wrote:
> July 26, 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 v4:
>> - Don't regenerate slot variable when we already had it.
>> 
>> Changes in v3:
>> - Commenting fixes requested by Seungwoon Jeon and Jaehoon Chung.
>> - Only pass 'slot' to the low power disable function since whole mmc
>>   structure wasn't needed.
>> 
>> 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 |   41 ++++++++++++++++++++++++++++++++++++++---
>>  1 files changed, 38 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>> index 72dc3cd..882748b 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 +865,30 @@ 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 the
>> + * description of the CLKENA register we should disable low power mode
>> + * for SDIO cards if we need SDIO interrupts to work.
>> + *
>> + * This function is fast if low power mode is already disabled.
>> + */
>> +static void dw_mci_disable_low_power(struct dw_mci_slot *slot)
>> +{
>> +	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 +898,14 @@ 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(slot);
>> +
>>  		mci_writel(host, INTMASK,
>>  			   (int_mask | SDMMC_INT_SDIO(slot->id)));
>>  	} else {
>
> Basically, disabling low power mode doesn't affect origin working.
> This patch will guarantees to supply the clock while sdio interrupt is activated.
> Looks good to me.
> Chris, feel free to add my ack.
>
> Acked-by: Seungwon Jeon <tgih.jun@...sung.com>

Thanks, pushed to mmc-next for 3.7.

- Chris.
-- 
Chris Ball   <cjb@...top.org>   <http://printf.net/>
One Laptop Per Child
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