dont write SPMODE reg unless mode changed.
it causes SPI to go hi-z momentarily
which can cause a spike on the CLK line
this is a problem in MMC where /CS is held asserted
across multiple transactions.
Signed-off-by: Mike Hench <[EMAIL PROTECTED]>
---
--- linux-2.6.25-rc5.orig/drivers/spi/spi_mpc83xx.c 2008-03-10
00:22:27.000000000 -0500
+++ linux-2.6.25-rc5/drivers/spi/spi_mpc83xx.c 2008-03-31
07:37:37.000000000 -0500
@@ -147,6 +147,7 @@
if (value == BITBANG_CS_ACTIVE) {
u32 regval =
mpc83xx_spi_read_reg(&mpc83xx_spi->base->mode);
+ u32 regval0 = regval;
u32 len = spi->bits_per_word;
u8 pm;
@@ -188,9 +189,16 @@
regval |= SPMODE_PM(pm);
}
- /* Turn off SPI unit prior changing mode */
- mpc83xx_spi_write_reg(&mpc83xx_spi->base->mode, 0);
- mpc83xx_spi_write_reg(&mpc83xx_spi->base->mode, regval);
+ // dont write reg unless mode changed.
+ // it causes SPI to go hi-z momentarily
+ // which can cause a spike on the CLK line
+ // this is a problem in MMC where /CS is held asserted
+ // across multiple transactions.
+ if(regval != regval0) {
+ /* Turn off SPI unit prior changing mode */
+ mpc83xx_spi_write_reg(&mpc83xx_spi->base->mode,
0);
+ mpc83xx_spi_write_reg(&mpc83xx_spi->base->mode,
regval);
+ }
if (mpc83xx_spi->activate_cs)
mpc83xx_spi->activate_cs(spi->chip_select, pol);
}
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