[PATCH 5/6] mmc: sdhci: calculate max_discard_to dynamically for SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK

[Dong Aisheng <b29396@freescale.com>]

For host controllers using SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK, since the card
clock is changed dynamically for different cards, it does not make sense
to use the maximum host clock to calculate max_discard_to which may lead
the max_discard_to to be much smaller than its capbility and affect the card
discard performance a lot.
e.g. the host clock is 200Mhz, but the card is working on 50Mhz. Then the
max_discard_to is only 1/4 of its real capbility.

In this patch, it uses the actual_clock to calculate the max_discard_to
dynamically as long as a new clock speed is set.

Tested with a high speed SDHC card shows:
Originally:
mmc1: new high speed SDHC card at address aaaa
mmc1: calculated max. discard sectors 49152 for timeout 1355 ms
Now:
mmc1: new high speed SDHC card at address aaaa
mmc1: calculated max. discard sectors 712704 for timeout 5422 ms
The max_discard_sectors will increase a lot which will also improve discard
performance a lot.

The one known limitation of this approach is that it does not cover the special
case for user changes the clock via sysfs, since the max_discard_to is only
initialised for one time during the mmc queue init.

Signed-off-by: Dong Aisheng <b29396@freescale.com>
---
 drivers/mmc/host/sdhci.c |   27 +++++++++++++++++++++------
 1 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 4cc3bd6..9be8a79 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1143,14 +1143,14 @@ static void sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
 	unsigned long timeout;
 
 	if (clock && clock == host->clock)
-		return;
+		goto out;
 
 	host->mmc->actual_clock = 0;
 
 	if (host->ops->set_clock) {
 		host->ops->set_clock(host, clock);
 		if (host->quirks & SDHCI_QUIRK_NONSTANDARD_CLOCK)
-			return;
+			goto out;
 	}
 
 	sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
@@ -1249,6 +1249,19 @@ clock_set:
 
 out:
 	host->clock = clock;
+
+	/* update timeout_clk and max_discard_to once the SDCLK is changed */
+	if (host->quirks & SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK && clock) {
+		host->timeout_clk = host->mmc->actual_clock ?
+					host->mmc->actual_clock / 1000 :
+					host->clock / 1000;
+		if (host->ops->get_max_timeout)
+			host->mmc->max_discard_to =
+					host->ops->get_max_timeout(host);
+		else
+			host->mmc->max_discard_to = (1 << 27) /
+					host->timeout_clk;
+	}
 }
 
 static inline void sdhci_update_clock(struct sdhci_host *host)
@@ -2939,10 +2952,12 @@ int sdhci_add_host(struct sdhci_host *host)
 	if (host->quirks & SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK)
 		host->timeout_clk = mmc->f_max / 1000;
 
-	if (host->ops->get_max_timeout)
-		mmc->max_discard_to = host->ops->get_max_timeout(host);
-	else
-		mmc->max_discard_to = (1 << 27) / host->timeout_clk;
+	if (!(host->quirks & SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK)) {
+		if (host->ops->get_max_timeout)
+			mmc->max_discard_to = host->ops->get_max_timeout(host);
+		else
+			mmc->max_discard_to = (1 << 27) / host->timeout_clk;
+	}
 
 	mmc->caps |= MMC_CAP_SDIO_IRQ | MMC_CAP_ERASE | MMC_CAP_CMD23;
 
-- 
1.7.2.rc3