lkml.org 
[lkml]   [2015]   [Oct]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH-v5 RESEND 4/5] Documentation: binding: add sclk adjustment properties to i2c-pxa
On Mon, Aug 24, 2015 at 11:29:37AM +0530, Vaibhav Hiremath wrote:
> With addition of PXA910 family of devices, the TWSI module supports
> new feature which allows us to adjust SCLK. i2c-pxa driver takes input
> configuration in nsec and converts it to respective bit-fields,
>
> - i2c-sclk-low-time-ns : SCLK low time (tlow)
> This property is used along with mode selection.
> - i2c-sclk-high-time-ns : SCLK high time (thigh)
> - i2c-start-hold-time-ns : Used in case of high speed mode for start bit
> hold/setup wait counter.
> - i2c-stop-hold-time-ns : Used in case of high speed mode for stop bit
> hold/setup wait counter.
> - i2c-sda-hold-time-ns : Used to calculate hold/setup wait counter for
> standard and fast mode.
>
> Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>

Ooookay, after checking some datasheets, I finally stumbled over the
fact that this driver is not using "clock-frequency" to determine the
bus speed. However, this is the standard way of defining that in DT, so
this driver should adhere to that, too, and not invent something new.
Previously, I was under the impression that the above parameters were
needed for fine-tuning and couldn't fully grasp why. But this is for
defining the bus speed which is a no-go.

It looks to me that older PXA only have a bit to select between 100 and
400kHz while this newer one can have arbitrary frequencies. Correct?

So, what the driver should do:

- Keep support for the old "mrvl,i2c-fast-mode" binding which should be
marked as deprecated

- get the value of the standard property "clock-frequency"

- for old PXAs, complain if not 100 or 400kHz, otherwise set the bit
accordingly

- for new PXAs, calculate the ilcr and iwcr values from
"clock-frequency"

Makes sense?

Regards,

Wolfram

[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2015-10-25 10:01    [W:0.566 / U:0.496 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site