mmc: core: fix performance regression initializing MMC host controllers

Commit fa5501890d8974301042e0202d342a6cbe8609f4 introduced a 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.

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>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

3 files changed, 5 insertions, 1 deletions

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 3bf1c462eded..c1893c9c3c31 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 2592dddbd965..7bcf74b1a5cd 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 17d714801e94..8873e8349597 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 */