Hello Eduardo, > -----Original Message----- > From: Eduardo Valentin [mailto:eduardo.valen...@nokia.com] > Sent: Wednesday, February 17, 2010 1:46 AM > To: Sonasath, Moiz > Cc: linux-omap@vger.kernel.org; sa...@linux.intel.com; t...@atomide.com; > Pais, Allen > Subject: Re: [PATCH 1/2] omap: Disable TWL4030/5030 I2C1/I2C4 internal > pull-ups > > Hello Moiz, > > On Wed, Feb 17, 2010 at 01:57:21AM +0100, ext Moiz Sonasath wrote: > > This patch disables TWL4030/5030 I2C1 adn I2C4(SR) internal pull-up, to > > use only the external HW resistor >=470 Ohm for the assured > > functionality in HS mode. > > > > While testing the I2C in High Speed mode, it was discovered that > > without a proper pull-up resistor, there is data corruption during > > multi-byte transfer. RTC(time_set) test case was used for testing. > > Nice findings! > > > > > >From the analysis done, it was concluded that ideally we need a > > pull-up of 1.6k Ohm(recomended) or atleast 470 Ohm or greater for > > assured performance in HS mode. > > > > Signed-off-by: Moiz Sonasath <m-sonas...@ti.com> > > Signed-off-by: Allen Pais <allen.p...@ti.com> > > --- > > drivers/mfd/twl-core.c | 13 +++++++++++++ > > include/linux/i2c/twl.h | 15 +++++++++++++++ > > 2 files changed, 28 insertions(+), 0 deletions(-) > > > > diff --git a/drivers/mfd/twl-core.c b/drivers/mfd/twl-core.c > > index 2a76065..35ae2ee 100644 > > --- a/drivers/mfd/twl-core.c > > +++ b/drivers/mfd/twl-core.c > > @@ -965,6 +965,7 @@ twl_probe(struct i2c_client *client, const struct > i2c_device_id *id) > > int status; > > unsigned i; > > struct twl4030_platform_data *pdata = client->dev.platform_data; > > + u8 temp; > > > > if (!pdata) { > > dev_dbg(&client->dev, "no platform data?\n"); > > @@ -1032,6 +1033,18 @@ twl_probe(struct i2c_client *client, const struct > i2c_device_id *id) > > goto fail; > > } > > > > + /* Disable TWL4030/TWL5030 I2C Pull-up on I2C1 and I2C4(SR) > interface. > > + * Program I2C_SCL_CTRL_PU(bit 0)=0, I2C_SDA_CTRL_PU (bit 2)=0, > > + * SR_I2C_SCL_CTRL_PU(bit 4)=0 and SR_I2C_SDA_CTRL_PU(bit 6)=0. > > + */ > > + > > + if (twl_class_is_4030()) { > > Is this run time check sufficient enough to determine if this fix must be > applied? > From what you have described on you patch description, looks like it is > supposed to be > only for HS mode. I don't know, maybe if you bind this to a platform / > board configuration > flag would it be better? I mean, you create a flag inside the platform > data to determine > if this fix must be applied or not. At least for me, having an external pu > resistor > seams to be very board dependent. >
>From what I observed, having a smaller pull-up (<470 OHM) resistor is >affecting HS mode operation. Moreover, irrespective of whatever external >pull-up value we have, if we have internal pull-up enabled, it comes in >parallel to the external pull-up and thereby reduces the effective pull-up on >the line. So it's safe to have a higher pull-up value instead rather than >having the internal pull-up enabled (irrespective of whatever the external >value is). Also, for all the OMAP boards that we have I think we always have >an external pull-up typically 470 ohm and hence if we just depend on that >external resistor without involving any of the internal pull-ups, HS/FS/LS >should just work fine. That was the whole idea. > > > + twl_i2c_read_u8(TWL4030_MODULE_INTBR, &temp, REG_GPPUPDCTR1); > > + temp &= ~(SR_I2C_SDA_CTRL_PU | SR_I2C_SCL_CTRL_PU | \ > > + I2C_SDA_CTRL_PU | I2C_SCL_CTRL_PU); > > + twl_i2c_write_u8(TWL4030_MODULE_INTBR, temp, REG_GPPUPDCTR1); > > + } > > + > > status = add_children(pdata, id->driver_data); > > fail: > > if (status < 0) > > diff --git a/include/linux/i2c/twl.h b/include/linux/i2c/twl.h > > index bf1c5be..fd95eca 100644 > > --- a/include/linux/i2c/twl.h > > +++ b/include/linux/i2c/twl.h > > @@ -239,6 +239,21 @@ int twl6030_interrupt_mask(u8 bit_mask, u8 offset); > > > > /*--------------------------------------------------------------------- > -*/ > > > > +/*Interface Bit Register (INTBR) offsets > > + *(Use TWL_4030_MODULE_INTBR) > > + */ > > + > > +#define REG_GPPUPDCTR1 0x0F > > + > > +/*I2C1 and I2C4(SR) SDA/SCL pull-up control bits */ > > + > > +#define I2C_SCL_CTRL_PU BIT(0) > > +#define I2C_SDA_CTRL_PU BIT(2) > > +#define SR_I2C_SCL_CTRL_PU BIT(4) > > +#define SR_I2C_SDA_CTRL_PU BIT(6) > > + > > +/*--------------------------------------------------------------------- > -*/ > > + > > /* > > * Keypad register offsets (use TWL4030_MODULE_KEYPAD) > > * ... SIH/interrupt only > > -- > > 1.5.6.3 > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-omap" in > > the body of a message to majord...@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > Eduardo Valentin -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
