There is an upcoming patch for core.c shown in the git tree shown below.
A standard sdhci.c controller running at 50MHz can divide the speed down to 50MHz/256 or 193000 bits/sec. This MINIMUM value is larger than the +#define MMC_INIT_FREQ 64000 and will invoke the error message in
static void mmc_power_up(struct mmc_host *host) in core.c
pr_warning("%s: Minimum clock frequency too high for "
"identification mode\n", mmc_hostname(host));
=======
The minimum value should be raised to a more appropriate value.
Philip
==== upcoming patch in git tree for 2.6.34 ===
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -907,12 +907,12 @@ static void mmc_power_up(struct mmc_host *host)
*/
mmc_delay(10);
- if (host->f_min > 400000) {
+ if (host->f_min > MMC_INIT_FREQ) {
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 = MMC_INIT_FREQ;
host->ios.power_mode = MMC_POWER_ON;
mmc_set_ios(host);
--- a/drivers/mmc/core/core.h
+++ b/drivers/mmc/core/core.h
@@ -15,6 +15,16 @@
#define MMC_CMD_RETRIES 3
+/* Spec says initialisation must happen at or below 400kHz.
+ * Some MMC cards fail to initialise at 400kHz (even as low as 200kHz) and
+ * Some host controllers (eg. tmio_mmc) cannot garantee to set the clock below
+ * 400kHz (it rounds to the closest clock freq available).
+ *
+ * 64 kHz seems like a good speed/reliability compromise.
+ */
+
+#define MMC_INIT_FREQ 64000
+
struct mmc_bus_ops {
int (*awake)(struct mmc_host *);
int (*sleep)(struct mmc_host *); --
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