Thanks and Best Regards Jerry Huang
> -----Original Message----- > From: u-boot-boun...@lists.denx.de [mailto:u-boot-boun...@lists.denx.de] > On Behalf Of Huang Changming-R66093 > Sent: Thursday, October 27, 2011 3:40 PM > To: Joakim Tjernlund > Cc: u-boot@lists.denx.de > Subject: Re: [U-Boot] [PATCH 2/2] Powerpc/i2c: Force i2c to become bus > master out of reset > > > > Thanks and Best Regards > Jerry Huang > > > > -----Original Message----- > > From: Joakim Tjernlund [mailto:joakim.tjernl...@transmode.se] > > Sent: Thursday, October 27, 2011 3:26 PM > > To: Huang Changming-R66093 > > Cc: u-boot@lists.denx.de > > Subject: Re: [U-Boot] [PATCH 2/2] Powerpc/i2c: Force i2c to become > bus > > master out of reset > > > > > From: <chang-ming.hu...@freescale.com> > > > > > > From: Jerry Huang <chang-ming.hu...@freescale.com> > > > > > > It is sometimes necessary to force the I2C module to become the I2C > > > bus master out of reset and drive SCL(even though SDA may already > be > > > driven, which indicates that the bus is busy). This can occur when > a > > > system reset does not cause all I2C devices to be reset. Thus, SDA > > can > > > be driven low by another I2C device while this I2C module is coming > > > out of reset and stays low indefinitely. The following procedure > can > > > be used to force this I2C module to generate SCL so that the device > > > driving SDA can finish its transaction. > > > > > > Signed-off-by: Jerry Huang <chang-ming.hu...@freescale.com> > > > --- > > > drivers/i2c/fsl_i2c.c | 18 ++++++++++++++++++ > > > 1 files changed, 18 insertions(+), 0 deletions(-) > > > > > > diff --git a/drivers/i2c/fsl_i2c.c b/drivers/i2c/fsl_i2c.c index > > > 258be0a..007db70 100644 > > > --- a/drivers/i2c/fsl_i2c.c > > > +++ b/drivers/i2c/fsl_i2c.c > > > @@ -252,6 +252,24 @@ i2c_init(int speed, int slaveadd) > > > writeb(slaveadd << 1, &dev->adr);/* write slave address */ > > > writeb(0x0, &dev->sr); /* clear status register */ > > > writeb(I2C_CR_MEN, &dev->cr); /* start I2C controller */ > > > + > > > + /* Force I2C module to become bus master which can occure > when > > > + * a system reset does not cause all I2C devices to be reset > > */ > > > + udelay(5); > > > + if (readb(&dev->sr) & I2C_SR_MBB) { > > > > You need to the sequence unconditionally, the slave can be stuck > > without driving SCL. > > > > > + writeb(I2C_CR_MSTA, &dev->cr); > > > + udelay(5); > > > + writeb(I2C_CR_MEN | I2C_CR_MSTA, &dev->cr); > > > + udelay(5); > > > + readb(&dev->dr); > > > + udelay(5); > > > + writeb(I2C_CR_MEN, &dev->cr); > > > + udelay(5); > > > + if (readb(&dev->sr) & I2C_SR_MBB) > > > + debug("I2C%d: Drive SCL failed\n", i + 1); > > > + else > > > + debug("I2C%d: Drive SCL succeed\n", i + 1); > > > + } > > > > The above sequence is different than the kernel version, why? > > I don't know the kernel version, but I write the u-boot code according > to the Reference Manual of PowerPC, e.g p1022: > 11.5.6 Generation of SCL When SDA Low > It is sometimes necessary to force the I2C module to become the I2C bus > master out of reset and drive SCL(even though SDA may already be driven, > which indicates that the bus is busy). This can occur when a system > reset does not cause all I2C devices to be reset. Thus, SDA can be > driven low by another I2C device while this I2C module is coming out of > reset and stays low indefinitely. The following procedure can be used > to force this I2C module to generate SCL so that the device driving SDA > can finish its transaction: > 1. Disable the I2C module and set the master bit by setting I2CCR to > 0x20 > 2. Enable the I2C module by setting I2CCR to 0xA0 > 3. Read the I2CDR > 4. Return the I2C module to slave mode by setting I2CCR to 0x80 > Compare with kernel version, the difference is one line: Uboot: readb(&dev->dr); Kernel has no any operation. But, I check the comment of kernel, because the 9th clock pulse isn't generated, the sequence of function mpc_i2c_fixup is needed to generate 9th clock pulse. _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
