Paul, > -----Original Message----- > From: Paul Walmsley [mailto:paul@xxxxxxxxx] > Sent: Monday, February 01, 2010 9:37 PM > To: Pais, Allen > Cc: linux-omap@xxxxxxxxxxxxxxx; Sonasath, Moiz; tony@xxxxxxxxxxx > Subject: Re: [PATCH 1/2] omap: Disable GAIA I2C1/I2C4 internal pull-ups > > Hi Allen, > > On Thu, 21 Jan 2010, Pais, Allen wrote: > > > This patch disables GAIA 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. > > > > >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. > > A few more questions. > > 1. Does this patch also apply to other TI PMICs, e.g., Triton2, Reno, etc? Thanks for raising this important question. This patch does hold true for the following PM IC's: Triton(TWL4030)/GAIA(TWL5030)/Phoenix(TWL6030) I did verify, the register 'REG_GPPUPDCTR1' holds true for Triton(TWL4030)/GAIA(TWL5030), hence for OMAP34XX/36XX. But there is a register change for this PU/PD control on Phoenix(TWL6030) which is used with OMAP44XX. So I might have to modify this patch a little as this code will apply for TWL4030/5030 and have to introduce new code to achieve the intended fix for TWL6030. I don't think so it applies to Reno though, AFAIK its not included in the Triton family and not used with OMAP on any boards. > > 2. It sounds like, from the patch description, that HS I2C mode is not > reliable on boards without external pullups. Shouldn't this patch (or one > in the same series) provide some way for mach-omap2/board-*.c files to > indicate this to the I2C code, such that HS I2C can be disallowed on those > boards? Similarly, for SmartReflex, which has an internal I2C controller > but does not use the OMAP I2C driver code, shouldn't there be a similar > mechanism for that code? Its not that HS I2C mode is not reliable without external pull-ups but what was observed is that, for reliable operation a HW resitor >= 470 Ohm is needed as pull-up. Now if we keep the internal pull-ups on PIC's enabled they come in parallel to the external pull-up and might lead to lower equivalent resistor value (< required 470 Ohm). That was the reason we decided to just rely on the external resistor on OMAP SOM, and disable any internal pull-ups on Power IC as well as on OMAP (36XX/44XX). > > > - Paul -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
