[PATCH] MMC Core: Drop initialization frequency floor to 50kHz

From: Ben Nizette
Date: Wed Jul 01 2009 - 19:51:07 EST


Patch

commit 8dfd0374be84793360db7fff2e635d2cd3bbcb21
Author: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
Date: Thu Apr 9 08:32:02 2009 +0200

MMC core: limit minimum initialization frequency to 400kHz

Was recently merged. This is too fast for at least one setup
permutation - the one on my desk which through trial and error won't
initialise at anything above ~350kHz (older Sandisk 256MB SD on
atmel-mci).

To avoid a string of "just found card X which requires clock
(current_clock - epsilon)" this patch drops the floor right down to
50kHz. This is about the slowest rate before which the discovery
process takes a noticeable slowdown.

Signed-off-by: Ben Nizette <bn@xxxxxxxxxxxxxxx>
---
diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index d84c880..6ee1931 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -708,12 +708,13 @@ 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;
+ /*
+ * Card discovery is typically done at the controller's minimum
+ * allowable frequency but for some controllers this is minimum
+ * is unreasonably slow. In that case we limit slow clock rate
+ * to 50KHz.
+ */
+ host->ios.clock = max(host->f_min, 50000);

host->ios.power_mode = MMC_POWER_ON;
mmc_set_ios(host);


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