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Subject[PATCH 4/6] atmel-mci: CLKDIV cap to restrict the MCI controller speed
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This patch adds the compile time configuration option for the atmel-mci driver to cap the MCI CLKDIV register value to a minimum value.

This is useful for debugging and for boards that have a long mci clock line.

Signed-off-by: Rob Emanuele <rob@emanuele.us>
---
drivers/mmc/host/Kconfig | 14 ++++++++++++++
drivers/mmc/host/atmel-mci.c | 10 ++++++++++
2 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
index 5875125..b628037 100644
--- a/drivers/mmc/host/Kconfig
+++ b/drivers/mmc/host/Kconfig
@@ -161,6 +161,20 @@ config MMC_ATMELMCI

endchoice

+config MMC_ATMELMCI_CLKDIV_CAP
+ int "Cap the CLKDIV to keep the controller from going too fast."
+ depends on MMC_ATMELMCI
+ default 0
+ range 0 255
+ help
+ This is the lowest value the clock divisor for the MMC
+ controller can be. Value is between 0 and 255.
+ MCI_CK = MCK/(2*(CLKDIV+1))
+ Raising this value may improve your controller's reliability
+ at the cost of speed.
+
+ If unsure, leave at 0.
+
config MMC_ATMELMCI_ALWAYS_RESET
bool "Reset before every request. Sometimes needed for buggy chips."
depends on MMC_ATMELMCI
diff --git a/drivers/mmc/host/atmel-mci.c b/drivers/mmc/host/atmel-mci.c
index e5894f6..601dae7 100644
--- a/drivers/mmc/host/atmel-mci.c
+++ b/drivers/mmc/host/atmel-mci.c
@@ -72,6 +72,10 @@ struct atmel_mci_dma {
#define MMC_ALWAYS_RESET 0
#endif

+#ifndef CONFIG_MMC_ATMELMCI_CLKDIV_CAP
+#define CONFIG_MMC_ATMELMCI_CLKDIV_CAP 0
+#endif
+
/**
* struct atmel_mci - MMC controller state shared between all slots
* @lock: Spinlock protecting the queue and associated data.
@@ -882,6 +886,12 @@ static void atmci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
clock_min, host->bus_hz / (2 * 256));
clkdiv = 255;
}
+ if (clkdiv < CONFIG_MMC_ATMELMCI_CLKDIV_CAP) {
+ dev_warn(&mmc->class_dev,
+ "clkdiv %u too fast; capped using %u\n",
+ clkdiv, CONFIG_MMC_ATMELMCI_CLKDIV_CAP);
+ clkdiv = CONFIG_MMC_ATMELMCI_CLKDIV_CAP;
+ }

host->mode_reg = MCI_MR_CLKDIV(clkdiv);

--
1.6.0.4


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