[PATCH] i2c: omap: improve duty cycle on SCL
balbi at ti.com
Thu Jun 18 10:24:28 PDT 2015
On Thu, Jun 18, 2015 at 08:39:11AM +0200, Michael Lawnick wrote:
> Am 17.06.2015 um 17:38 schrieb Felipe Balbi:
> >On Wed, Jun 17, 2015 at 01:09:53PM +0200, Michael Lawnick wrote:
> >>Am 16.06.2015 um 21:17 schrieb Felipe Balbi:
> >>>With this patch we try to be as close to 50%
> >>>duty cycle as possible. The reason for this
> >>>is that some devices present an erratic behavior
> >>>with certain duty cycles.
> >>>One such example is TPS65218 PMIC which fails
> >>>to change voltages when running @ 400kHz and
> >>>duty cycle is lower than 34%.
> >>>The idea of the patch is simple:
> >>>calculate desired scl_period from requested scl
> >>>and use 50% for tLow and 50% for tHigh.
> >>Hmm, and what's about Philips I2C specification 2.1, Jan 2000, Table 5?
> >>>PARAMETER SYMBOL STANDARD-MODE FAST-MODE UNIT
> >>> MIN. MAX. MIN. MAX.
> >>>LOW period of the SCL clock tLOW 4.7 – 1.3 – µs
> >>>HIGH period of the SCL clock tHIGH 4.0 – 0.6 – µs
> >>Your signal is in spec (0.85 µs high, 1,65 low).
> >>Maybe your TPS65218 is just buggy or signals are bad?
> >yes, tps is buggy, it's written in the commit log itself.
> So I think it is unacceptable to change the adapters code violating
> specification because some buggy device doesn't work properly.
read the other thread and you'll see that it's not violating jack
> This change for your device has chance to blow up many correctly
> working ones.
-------------- next part --------------
A non-text attachment was scrubbed...
Size: 819 bytes
Desc: Digital signature
More information about the linux-arm-kernel