[PATCH V2 1/3] mmc: add support for H/W clock gating of SD controller

[PATCH V2 1/3] mmc: add support for H/W clock gating of SD controller

[Philip Rakity]

This code extends software clock gating in the MMC layer by adding the ability
to indicate that the SD controller supports hardware clock gating.

Hardware clock gating is enabled by setting the MMC capability
MMC_CAP_HW_CLOCK_GATING in the SD driver.

eg: host->mmc->caps |= MMC_CAP_HW_CLOCK_GATING

The approach follows the suggestion of Nico Pitre.

SD/MMC/eMMC cards use dynamic clocks
SDIO uses continuous clocks to properly detect SDIO card interrupts

The code has been tested using marvell linux for MMP2.  The Marvell
controller support H/W clock gating.

Signed-off-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Mark F. Brown <markb@marvell.com>
---
 drivers/mmc/core/core.c  |   32 ++++++++++++++++++++++++++++++++
 drivers/mmc/core/core.h  |   13 +++++++++++++
 drivers/mmc/core/host.c  |   14 +++++++++++++-
 include/linux/mmc/host.h |    1 +
 4 files changed, 59 insertions(+), 1 deletions(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 6286898..de867d1 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -682,6 +682,28 @@ void mmc_ungate_clock(struct mmc_host *host)
 	}
 }
 
+/*
+ * Let hardware automatically gate the clock when the card becomes idle
+ */
+void mmc_hwgate_clock(struct mmc_host *host)
+{
+	if (host->caps & MMC_CAP_HW_CLOCK_GATING) {
+		host->clk_gated = true;
+		mmc_set_ios(host);
+	}
+}
+
+/*
+ * This ungates the clock by turning off h/w gating
+ */
+void mmc_hwungate_clock(struct mmc_host *host)
+{
+	if (host->caps & MMC_CAP_HW_CLOCK_GATING) {
+		host->clk_gated = false;
+		mmc_set_ios(host);
+	}
+}
+
 void mmc_set_ungated(struct mmc_host *host)
 {
 	unsigned long flags;
@@ -1548,6 +1570,8 @@ void mmc_rescan(struct work_struct *work)
 			mmc_hostname(host), __func__, host->f_init);
 #endif
 		mmc_power_up(host);
+
+		mmc_hwungate_clock(host);
 		sdio_reset(host);
 		mmc_go_idle(host);
 
@@ -1569,6 +1593,10 @@ void mmc_rescan(struct work_struct *work)
 
 				if (mmc_attach_sd(host, ocr))
 					mmc_power_off(host);
+
+				/* hw clock gating is off when we get here */
+				/* do not enable clock gating for sdio cards */
+				/* sdio cards can miss interrupts */
 			}
 			goto out;
 		}
@@ -1580,6 +1608,8 @@ void mmc_rescan(struct work_struct *work)
 		if (!err) {
 			if (mmc_attach_sd(host, ocr))
 				mmc_power_off(host);
+			else
+				mmc_hwgate_clock(host);
 			goto out;
 		}
 
@@ -1590,6 +1620,8 @@ void mmc_rescan(struct work_struct *work)
 		if (!err) {
 			if (mmc_attach_mmc(host, ocr))
 				mmc_power_off(host);
+			else
+				mmc_hwgate_clock(host);
 			goto out;
 		}
 
diff --git a/drivers/mmc/core/core.h b/drivers/mmc/core/core.h
index 026c975..3810e28 100644
--- a/drivers/mmc/core/core.h
+++ b/drivers/mmc/core/core.h
@@ -35,6 +35,19 @@ void mmc_set_chip_select(struct mmc_host *host, int mode);
 void mmc_set_clock(struct mmc_host *host, unsigned int hz);
 void mmc_gate_clock(struct mmc_host *host);
 void mmc_ungate_clock(struct mmc_host *host);
+
+#ifdef CONFIG_MMC_CLKGATE
+void mmc_hwgate_clock(struct mmc_host *host);
+void mmc_hwungate_clock(struct mmc_host *host);
+#else
+static inline void mmc_hwgate_clock(struct mmc_host *host)
+{
+}
+
+static inline void mmc_hwungate_clock(struct mmc_host *host)
+{
+}
+#endif
 void mmc_set_ungated(struct mmc_host *host);
 void mmc_set_bus_mode(struct mmc_host *host, unsigned int mode);
 void mmc_set_bus_width(struct mmc_host *host, unsigned int width);
diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
index 92e3370..afadcf4 100644
--- a/drivers/mmc/core/host.c
+++ b/drivers/mmc/core/host.c
@@ -130,6 +130,9 @@ void mmc_host_clk_ungate(struct mmc_host *host)
 {
 	unsigned long flags;
 
+	if (host->caps & MMC_CAP_HW_CLOCK_GATING)
+		return;
+
 	mutex_lock(&host->clk_gate_mutex);
 	spin_lock_irqsave(&host->clk_lock, flags);
 	if (host->clk_gated) {
@@ -178,10 +181,13 @@ void mmc_host_clk_gate(struct mmc_host *host)
 {
 	unsigned long flags;
 
+	if (host->caps & MMC_CAP_HW_CLOCK_GATING)
+		return;
+
 	spin_lock_irqsave(&host->clk_lock, flags);
 	host->clk_requests--;
 	if (mmc_host_may_gate_card(host->card) &&
-	    !host->clk_requests)
+		!host->clk_requests)
 		schedule_work(&host->clk_gate_work);
 	spin_unlock_irqrestore(&host->clk_lock, flags);
 }
@@ -212,6 +218,9 @@ unsigned int mmc_host_clk_rate(struct mmc_host *host)
  */
 static inline void mmc_host_clk_init(struct mmc_host *host)
 {
+	if (host->caps & MMC_CAP_HW_CLOCK_GATING)
+		return;
+
 	host->clk_requests = 0;
 	/* Hold MCI clock for 8 cycles by default */
 	host->clk_delay = 8;
@@ -231,6 +240,9 @@ static inline void mmc_host_clk_exit(struct mmc_host *host)
 	 * Wait for any outstanding gate and then make sure we're
 	 * ungated before exiting.
 	 */
+	if (host->caps & MMC_CAP_HW_CLOCK_GATING)
+		return;
+
 	if (cancel_work_sync(&host->clk_gate_work))
 		mmc_host_clk_gate_delayed(host);
 	if (host->clk_gated)
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 078cff7..243c7ab 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -171,6 +171,7 @@ struct mmc_host {
 #define MMC_CAP_POWER_OFF_CARD	(1 << 13)	/* Can power off after boot */
 
 #define MMC_CAP_BUS_WIDTH_TEST	(1 << 14)	/* CMD14/CMD19 bus width ok */
+#define MMC_CAP_HW_CLOCK_GATING	(1 << 15)	/* h/w supports clock gating */
 	mmc_pm_flag_t		pm_caps;	/* supported pm features */
 
 #ifdef CONFIG_MMC_CLKGATE
-- 
1.6.0.4

Re: [PATCH V2 1/3] mmc: add support for H/W clock gating of SD controller

[Nicolas Pitre]

On Tue, 7 Dec 2010, Philip Rakity wrote:

> 
> This code extends software clock gating in the MMC layer by adding the ability
> to indicate that the SD controller supports hardware clock gating.
> 
> Hardware clock gating is enabled by setting the MMC capability
> MMC_CAP_HW_CLOCK_GATING in the SD driver.
> 
> eg: host->mmc->caps |= MMC_CAP_HW_CLOCK_GATING
> 
> The approach follows the suggestion of Nico Pitre.
> 
> SD/MMC/eMMC cards use dynamic clocks
> SDIO uses continuous clocks to properly detect SDIO card interrupts
> 
> The code has been tested using marvell linux for MMP2.  The Marvell
> controller support H/W clock gating.
> 
> Signed-off-by: Philip Rakity <prakity@marvell.com>
> Signed-off-by: Mark F. Brown <markb@marvell.com>

There is one needless change in your patch:

> @@ -178,10 +181,13 @@ void mmc_host_clk_gate(struct mmc_host *host)
>  {
>  	unsigned long flags;
>  
> +	if (host->caps & MMC_CAP_HW_CLOCK_GATING)
> +		return;
> +
>  	spin_lock_irqsave(&host->clk_lock, flags);
>  	host->clk_requests--;
>  	if (mmc_host_may_gate_card(host->card) &&
> -	    !host->clk_requests)
> +		!host->clk_requests)

The second line of the if() was properly aligned before.

Other than that...

Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>


Nicolas