VIM3 - A311D - I2C AO Clock Questions

[Lucas Tanure]

On Mon, Mar 7, 2022 at 8:29 AM Neil Armstrong <narmstrong at baylibre.com> wrote:
>
> Hi,
>
> On 06/03/2022 11:23, Lucas Tanure wrote:
> > Hi,
> >
> > I am trying to integrate an I2C device into VIM3 using the I2C_AO bus.
> > My device uses a 100000Hz clock, but after changing
> > meson-g12b-a311d-khadas-vim3.dts to add my I2C node the driver could
> > not properly read its registers.
> >
> > It reads 0x9100, but the correct data should be 0xcb58.
> > The first thing I saw on the bus was that the frequency I requested by
> > the device tree was being set after the probe of my driver already
> > failed.
> > For that, I sent "i2c: meson: Fix wrong speed use from probe" which
> > fixes that issue.
> >
> > But I still get the wrong data, so my next guess is that the clock
> > duty cycle is 30%, and I think should be 50%.
> > Here is an image of the signals of the bus:
> > https://pasteboard.co/TEoxQucsXUUD.png
> >
> > I have tested other frequencies and all of them uses a 30% duty cycle,
> > where SCL is up 30% and low for 70% of the period.
>
> Indeed it seems by default the duty cycle is for Fast Mode, but standard mode should
> be around 50%. Did you try 400khz ?

Yes, 400Khz has the same issue of 30% duty cycle.

>
> Amlogic did some changes on their off-tree linux fork, please look around:
> https://github.com/khadas/linux/blob/khadas-vims-5.4.y-fc/drivers/i2c/busses/i2c-meson.c#L143

Thanks! I am investigating that code, but so far doesn't work.

>
> I'm unsure when REG_SLAVE_ADDR BIT(28) appeared, but if you try to port this upstream,
> we'll be happy to review it for inclusion.

I will try to get this working and push a patch.
Thanks
Lucas

>
> Neil
>
> >
> > Is possible to configure the clock to be 100000Hz, but with a 50% duty
> > cycle for this I2C bus on A3111D?
> >
> > Thanks
> > Lucas Tanure
> >
> > _______________________________________________
> > linux-amlogic mailing list
> > linux-amlogic at lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-amlogic