[PATCH V4 2/2] mmc: core: fix performance regression initializing MMC host controllers

Adrian Hunter
2013-04-08T10:44:20Z

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>
---

Changes for V4:
- use mmc_power_off() for MMC_CAP2_NO_PRESCAN_POWERUP
- add MMC_CAP2_NO_PRESCAN_POWERUP to sdhci-pci.c also

drivers/mmc/core/core.c | 5 ++++-
drivers/mmc/host/sdhci-acpi.c | 2 ++
drivers/mmc/host/sdhci-pci.c | 1 +
include/linux/mmc/host.h | 1 +
4 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 3bf1c46..65f9ca7 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -2416,7 +2416,10 @@ 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_off(host);
+ else
+ 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/drivers/mmc/host/sdhci-pci.c b/drivers/mmc/host/sdhci-pci.c
index c1f0372..0012d3f 100644
--- a/drivers/mmc/host/sdhci-pci.c
+++ b/drivers/mmc/host/sdhci-pci.c
@@ -1280,6 +1280,7 @@ static struct sdhci_pci_slot *sdhci_pci_probe_slot(

host->mmc->pm_caps = MMC_PM_KEEP_POWER | MMC_PM_WAKE_SDIO_IRQ;
host->mmc->slotno = slotno;
+ host->mmc->caps2 |= MMC_CAP2_NO_PRESCAN_POWERUP;

ret = sdhci_add_host(host);
if (ret)
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