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Subject[patch 4/4] sdio: disable CD resistor
-- 
David Vrabel, Software Engineer, Drivers group Tel: +44 (0)1223 692562
CSR plc, Churchill House, Cambridge Business Park, Cowley Road, CB4 0WZ


.
sdio: disable CD resistor

Disable the card detect resistor to ensure all data lines are equally loaded.
Not doing this can have a negative impact on buses with marginal signal
quality.

Signed-off-by: David Vrabel <david.vrabel@csr.com
---
Index: mmc/drivers/mmc/core/sdio.c
===================================================================
--- mmc.orig/drivers/mmc/core/sdio.c 2007-08-07 07:27:31.000000000 +0100
+++ mmc/drivers/mmc/core/sdio.c 2007-08-07 07:30:58.000000000 +0100
@@ -148,10 +148,25 @@
return ret;
}

+static int sdio_modify_cccr(struct mmc_card *card, unsigned reg,
+ u8 val, u8 mask)
+{
+ u8 old;
+ int ret;
+
+ ret = mmc_io_rw_direct(card, 0, 0, reg, 0, &old);
+ if (ret)
+ return ret;
+
+ val = (old & ~mask) | val;
+
+ ret = mmc_io_rw_direct(card, 1, 0, reg, val, NULL);
+ return ret;
+}
+
static int sdio_enable_wide(struct mmc_card *card)
{
int ret;
- u8 ctrl;

if (!(card->host->caps & MMC_CAP_4_BIT_DATA))
return 0;
@@ -159,13 +174,8 @@
if (card->cccr.low_speed && !card->cccr.wide_bus)
return 0;

- ret = mmc_io_rw_direct(card, 0, 0, SDIO_CCCR_IF, 0, &ctrl);
- if (ret)
- return ret;
-
- ctrl |= SDIO_BUS_WIDTH_4BIT;
-
- ret = mmc_io_rw_direct(card, 1, 0, SDIO_CCCR_IF, ctrl, NULL);
+ ret = sdio_modify_cccr(card, SDIO_CCCR_IF, SDIO_BUS_WIDTH_4BIT,
+ SDIO_BUS_WIDTH_MASK);
if (ret)
return ret;

@@ -334,6 +344,15 @@
mmc_set_clock(host, card->cis.max_dtr);

/*
+ * Disable Card Detect resistor on DAT3 so all data lines are
+ * loaded the same.
+ */
+ err = sdio_modify_cccr(card, SDIO_CCCR_IF, SDIO_BUS_CD_DISABLE,
+ SDIO_BUS_CD_DISABLE);
+ if (err)
+ goto remove;
+
+ /*
* Switch to wider bus (if supported).
*/
err = sdio_enable_wide(card);
Index: mmc/include/linux/mmc/sdio.h
===================================================================
--- mmc.orig/include/linux/mmc/sdio.h 2007-08-07 07:27:30.000000000 +0100
+++ mmc/include/linux/mmc/sdio.h 2007-08-07 07:27:31.000000000 +0100
@@ -94,6 +94,7 @@

#define SDIO_BUS_WIDTH_1BIT 0x00
#define SDIO_BUS_WIDTH_4BIT 0x02
+#define SDIO_BUS_WIDTH_MASK 0x03

#define SDIO_BUS_CD_DISABLE 0x80 /* disable pull-up on DAT3 (pin 1) */
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