[PATCH V3 2/2] mmc: core: fix performance regression initializing MMC host controllers

[Adrian Hunter <adrian.hunter@intel.com>]

Commit fa5501890d8974301042e0202d342a6cbe8609f4 introduced a boot time
performance regression by adding mmc_power_up() to mmc_start_host().
mmc_power_up() is not necessary to host controller initialization, it is
part of card initialization and is performed anyway asynchronously.
Please see the original commit for an explanation of the use of
mmc_power_up() in mmc_start_host().

This patch allows a driver to leave the power up in asynchronous code
(as it was before).

On my current target platform this reduces driver initialization from:

[    1.313220] initcall sdhci_acpi_driver_init+0x0/0x12 returned 0 after 102008 usecs

to this:

[    1.217209] initcall sdhci_acpi_driver_init+0x0/0x12 returned 0 after 8331 usecs

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 drivers/mmc/core/core.c       | 3 ++-
 drivers/mmc/host/sdhci-acpi.c | 2 ++
 include/linux/mmc/host.h      | 1 +
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 3bf1c46..c1893c9 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -2416,7 +2416,8 @@ void mmc_start_host(struct mmc_host *host)
 {
 	host->f_init = max(freqs[0], host->f_min);
 	host->rescan_disable = 0;
-	mmc_power_up(host);
+	if (!(host->caps2 & MMC_CAP2_NO_PRESCAN_POWERUP))
+		mmc_power_up(host);
 	mmc_detect_change(host, 0);
 }
 
diff --git a/drivers/mmc/host/sdhci-acpi.c b/drivers/mmc/host/sdhci-acpi.c
index 2592ddd..7bcf74b 100644
--- a/drivers/mmc/host/sdhci-acpi.c
+++ b/drivers/mmc/host/sdhci-acpi.c
@@ -195,6 +195,8 @@ static int sdhci_acpi_probe(struct platform_device *pdev)
 		host->mmc->pm_caps  |= c->slot->pm_caps;
 	}
 
+	host->mmc->caps2 |= MMC_CAP2_NO_PRESCAN_POWERUP;
+
 	err = sdhci_add_host(host);
 	if (err)
 		goto err_free;
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 17d7148..8873e83 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -280,6 +280,7 @@ struct mmc_host {
 #define MMC_CAP2_PACKED_WR	(1 << 13)	/* Allow packed write */
 #define MMC_CAP2_PACKED_CMD	(MMC_CAP2_PACKED_RD | \
 				 MMC_CAP2_PACKED_WR)
+#define MMC_CAP2_NO_PRESCAN_POWERUP (1 << 14)	/* Don't power up before scan */
 
 	mmc_pm_flag_t		pm_caps;	/* supported pm features */
 
-- 
1.7.11.7