Re: [PATCH] mpc83xx SPI glitch
flat view
From: Joakim Tjernlund <hidden>
Date: 2008-03-31 13:23:51
Mike
I already sent a patch some time ago, it addresses this bug and
alot more. See spi-devel-general
[off-list ref],
I am waiting for David B. to comment/apply it. If you want to see this
in 2.6.25 I suggest you remind 'David Brownell' [off-list ref]
Jocke
On Mon, 2008-03-31 at 08:04 -0500, Mike Hench wrote:quoted hunk ↗ jump to hunk
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. =20 Signed-off-by: Mike Hench <redacted> =20 --- =20--- linux-2.6.25-rc5.orig/drivers/spi/spi_mpc83xx.c 2008-03-1000:22:27.000000000 -0500+++ linux-2.6.25-rc5/drivers/spi/spi_mpc83xx.c 2008-03-3107:37:37.000000000 -0500@@ -147,6 +147,7 @@=20 if (value =3D=3D BITBANG_CS_ACTIVE) { u32 regval =3D mpc83xx_spi_read_reg(&mpc83xx_spi->base->mode); + u32 regval0 =3D regval; u32 len =3D spi->bits_per_word; u8 pm; =20@@ -188,9 +189,16 @@ regval |=3D SPMODE_PM(pm); }=20 - /* 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 !=3D 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); } =20 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev =20 =20