mmc: Make ID freq configurable

In the latest releases of the mmc driver, the freq during initialization
is set to a fixed 400 Khz.  This was reportedly too fast for several
users.  As there doesn't seem to be an ideal frequency
which-works-for-all, Pierre suggested to let the driver try several
frequencies.

This patch implements that idea. It will try mmc-initialization using
several frequencies from an array 400, 300, 200 and 100.

In case SDIO is broken, it'll still try to detect SDMEM, also at different
freqs.
Signed-off-by: Hein Tibosch <hein_tibosch@yahoo.es>
Cc: Pierre Ossman <pierre@ossman.eu>
Reviewed-by: Chris Ball <cjb@laptop.org>
Tested-by: Chris Ball <cjb@laptop.org>
Cc: Ben Nizette <bn@niasdigital.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Adrian Hunter <adrian.hunter@nokia.com>
Cc: Matt Fleming <matt@console-pimps.org>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/core.c

@@ -908,12 +908,7 @@ static void mmc_power_up(struct mmc_host *host)
 	 */
 	mmc_delay(10);
 
-	if (host->f_min > 400000) {
-		pr_warning("%s: Minimum clock frequency too high for "
-				"identification mode\n", mmc_hostname(host));
-		host->ios.clock = host->f_min;
-	} else
-		host->ios.clock = 400000;
+	host->ios.clock = host->f_init;
 
 	host->ios.power_mode = MMC_POWER_ON;
 	mmc_set_ios(host);
@@ -1405,6 +1400,8 @@ void mmc_rescan(struct work_struct *work)
 	u32 ocr;
 	int err;
 	unsigned long flags;
+	int i;
+	const unsigned freqs[] = { 400000, 300000, 200000, 100000 };
 
 	spin_lock_irqsave(&host->lock, flags);
 
@@ -1444,8 +1441,20 @@ void mmc_rescan(struct work_struct *work)
 	if (host->ops->get_cd && host->ops->get_cd(host) == 0)
 		goto out;
 
+	for (i = 0; i < ARRAY_SIZE(freqs); i++) {
 		mmc_claim_host(host);
 
+		if (freqs[i] >= host->f_min)
+			host->f_init = freqs[i];
+		else if (!i || freqs[i-1] > host->f_min)
+			host->f_init = host->f_min;
+		else {
+			mmc_release_host(host);
+			goto out;
+		}
+		pr_info("%s: %s: trying to init card at %u Hz\n",
+			mmc_hostname(host), __func__, host->f_init);
+
 		mmc_power_up(host);
 		sdio_reset(host);
 		mmc_go_idle(host);
@@ -1459,7 +1468,10 @@ void mmc_rescan(struct work_struct *work)
 		if (!err) {
 			if (mmc_attach_sdio(host, ocr)) {
 				mmc_claim_host(host);
-			/* try SDMEM (but not MMC) even if SDIO is broken */
+				/*
+				 * Try SDMEM (but not MMC) even if SDIO
+				 * is broken.
+				 */
 				if (mmc_send_app_op_cond(host, 0, &ocr))
 					goto out_fail;
 
@@ -1492,7 +1504,7 @@ void mmc_rescan(struct work_struct *work)
 out_fail:
 		mmc_release_host(host);
 		mmc_power_off(host);
-
+	}
 out:
 	if (host->caps & MMC_CAP_NEEDS_POLL)
 		mmc_schedule_delayed_work(&host->detect, HZ);

include/linux/mmc/host.h

@@ -123,6 +123,7 @@ struct mmc_host {
 	const struct mmc_host_ops *ops;
 	unsigned int		f_min;
 	unsigned int		f_max;
+	unsigned int		f_init;
 	u32			ocr_avail;
 	struct notifier_block	pm_notify;