[PATCH 3/3] mmc: omap_hsmmc: switch to 1-bit before turning off clocks if interrupts expected.

[NeilBrown <neilb@suse.de>]

According to section 7.1.2 of

http://www.sandisk.com/media/File/OEM/Manuals/SD_SDIO_specsv1.pdf

    In the case where the interrupt mechanism is used to wake the host while
    the card is in a low power state (i.e. no clocks), Both the card and the
    host shall be placed into the 1-bit SD mode prior to stopping the clock.


This is particularly important for the Marvell "libertas" wifi chip
in the GTA04.  While in 4-bit mode it will only signal an interrupt
when the clock is running (which is why setting CLKEXTFREE is
important).
In 1-bit mode, the interrupt is asynchronous (explained in OMAP3
TRM description of the CIRQ flag to MMCHS_STAT:

  In 1-bit mode, interrupt source is asynchronous (can be a source of
  asynchronous wakeup).
  In 4-bit mode, interrupt source is sampled during the interrupt
  cycle.

)

We cannot simply set 1-bit mode in omap_hsmmc_runtime_suspend
as that is called under a spinlock, and setting 1-bit mode requires
a sleeping call to the card.

So:
 - use a work_struct to schedule setting of 1-bit mode
 - intro a 'force_narrow' state flag which transitions:
     0 -> NARROW_PENDING -> NARROW_FORCED -> 0
 - have omap_hsmmc_runtime_suspend fail if interrupts are expected
   but bus is not in 1-bit mode.  When it fails it schedules
   the work to change the width. and sets NARROW_PENDING
 - when the host is claimed, if NARROW_FORCED is set, restore the
   4-bit bus
 - When the host is released (disable_fclk), if NARROW_FORCED,
   then suspend immediately, no autosuspend.  If NARROW_PENDING,
   clear that flag as the device has obviously just been used.

This all allows a graceful and race-free switch to 1-bit mode
before switching off the clocks, if interrupts are enabled.

With this, I can use my libertas wifi with a 4-bit bus, with
interrupts and runtime power-management enabled, and get around
14Mb/sec throughput (which is the best I've seen).

Signed-off-by: NeilBrown <neil@brown.name>
---
 drivers/mmc/host/omap_hsmmc.c |   55 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
index f84cfb01716d..91ddebbec8a3 100644
--- a/drivers/mmc/host/omap_hsmmc.c
+++ b/drivers/mmc/host/omap_hsmmc.c
@@ -214,6 +214,10 @@ struct omap_hsmmc_host {
 	int			reqs_blocked;
 	int			use_reg;
 	int			req_in_progress;
+	int			force_narrow;
+#define NARROW_PENDING	1
+#define NARROW_FORCED	2
+	struct work_struct	width_work;
 	unsigned long		clk_rate;
 	unsigned int		flags;
 #define AUTO_CMD23		(1 << 0)        /* Auto CMD23 support */
@@ -1778,12 +1782,43 @@ static void omap_hsmmc_conf_bus_power(struct omap_hsmmc_host *host)
 	set_sd_bus_power(host);
 }
 
+static void omap_hsmmc_width_work(struct work_struct *work)
+{
+	struct omap_hsmmc_host *host = container_of(work,
+						    struct omap_hsmmc_host,
+						    width_work);
+	atomic_t noblock;
+
+	atomic_set(&noblock, 1);
+	if (__mmc_claim_host(host->mmc, &noblock)) {
+		/* Device active again */
+		host->force_narrow = 0;
+		return;
+	}
+	if (host->force_narrow != NARROW_PENDING) {
+		/* Someone claimed and released before we got here */
+		mmc_release_host(host->mmc);
+		return;
+	}
+	if (sdio_disable_wide(host->mmc->card) == 0)
+		host->force_narrow = NARROW_FORCED;
+	else
+		host->force_narrow = 0;
+	mmc_release_host(host->mmc);
+}
+
 static int omap_hsmmc_enable_fclk(struct mmc_host *mmc)
 {
 	struct omap_hsmmc_host *host = mmc_priv(mmc);
 
 	pm_runtime_get_sync(host->dev);
 
+	if (host->force_narrow == NARROW_FORCED) {
+		if (sdio_enable_4bit_bus(mmc->card) > 0)
+			mmc_set_bus_width(mmc, MMC_BUS_WIDTH_4);
+		host->force_narrow = 0;
+	}
+
 	return 0;
 }
 
@@ -1791,8 +1826,13 @@ static int omap_hsmmc_disable_fclk(struct mmc_host *mmc)
 {
 	struct omap_hsmmc_host *host = mmc_priv(mmc);
 
-	pm_runtime_mark_last_busy(host->dev);
-	pm_runtime_put_autosuspend(host->dev);
+	if (host->force_narrow == NARROW_FORCED) {
+		pm_runtime_put_sync(host->dev);
+	} else {
+		host->force_narrow = 0;
+		pm_runtime_mark_last_busy(host->dev);
+		pm_runtime_put_autosuspend(host->dev);
+	}
 
 	return 0;
 }
@@ -2024,6 +2064,7 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
 	host->power_mode = MMC_POWER_OFF;
 	host->next_data.cookie = 1;
 	host->pbias_enabled = 0;
+	INIT_WORK(&host->width_work, omap_hsmmc_width_work);
 
 	ret = omap_hsmmc_gpio_init(mmc, host, pdata);
 	if (ret)
@@ -2311,6 +2352,16 @@ static int omap_hsmmc_runtime_suspend(struct device *dev)
 	spin_lock_irqsave(&host->irq_lock, flags);
 	if ((host->mmc->caps & MMC_CAP_SDIO_IRQ) &&
 	    (host->flags & HSMMC_SDIO_IRQ_ENABLED)) {
+		if (host->mmc->ios.bus_width != MMC_BUS_WIDTH_1) {
+			/* In 4-bit mode the card need the clock
+			 * to deliver interrupts, so it isn't safe
+			 * to turn it off.
+			 */
+			host->force_narrow = NARROW_PENDING;
+			schedule_work(&host->width_work);
+			ret = -EBUSY;
+			goto abort;
+		}
 		/* disable sdio irq handling to prevent race */
 		OMAP_HSMMC_WRITE(host->base, ISE, 0);
 		OMAP_HSMMC_WRITE(host->base, IE, 0);