[PATCH 4/6] Unified AVR32/AT91 MCI Driver Clock Divisor Cap

[Rob Emanuele <poorarm@shoreis.com>]

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.

Please read the whole set, try it out, and comment.

Thank you,

Rob Emanuele

---
 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 9e24029..9f797b2 100644
--- a/drivers/mmc/host/Kconfig
+++ b/drivers/mmc/host/Kconfig
@@ -150,6 +150,20 @@ 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 b133baa..1c1a4b3 100644
--- a/drivers/mmc/host/atmel-mci.c
+++ b/drivers/mmc/host/atmel-mci.c
@@ -74,6 +74,10 @@ 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.
@@ -876,6 +880,12 @@ 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;
- Show quoted text -
+               }

               host->mode_reg = MCI_MR_CLKDIV(clkdiv);

--
1.6.0.4
--
Robert Emanuele
Crystalfontz America, Inc.
www.crystalfontz.com
rje@crystalfontz.com
+1 509 892 1200