Re: [PATCH] iio: adc: max9611: Defer probe on POR read

Geert Uytterhoeven
2019-11-10T18:45:51Z

On Thu, Oct 17, 2019 at 2:55 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> On Wed, Oct 16, 2019 at 12:23 PM Jacopo Mondi <jacopo+renesas@jmondi.org> wrote:
> > The max9611 driver tests communications with the chip by reading the die
> > temperature during the probe function. If the temperature register
> > POR (power-on reset) value is returned from the test read, defer probe to
> > give the chip a bit more time to properly exit from reset.
> >
> > Reported-by: Geert Uytterhoeven <geert+renesas@glider.be>
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
>
> Thanks for your patch!
>
> > Geert,
> > I've not been able to reproduce the issue on my boards (M3-N
> > Salvator-XS and M3-W Salvator-X). As you reported the issue you might be
> > able to reproduce it, could you please test this?
>
> I can reproduce it on Salvator-XS with R-Car H3 ES2.0.
> According to my logs, I've seen the issue on all Salvator-X(S) boards,
> but not with the same frequency. Probability is highest on H3 ES2.0
> (ca. 5% of the boots since I first saw the issue), followed by H3 ES1.0,
> M3-W, and M3-N.
>
> After more investigation, my findings are:
> 1. I cannot reproduce the issue if the max9611 driver is modular.
> Is it related to using max9611 "too soon" after i2c bus init?
> How can "i2c bus init" impact a slave device?
> Perhaps due to pin configuration, e.g. changing from another pin
> function or GPIO to function i2c4?
> 2. Adding a delay at the top of max9611_init() fixes the issue.
> This would explain why the issue is less likely to happy on slower
> SoCs like M3-N.
> 3. Disabling all other i2c slaves on i2c4 in DTS fixes the issue.
> Before, max9611 was initialized last, so this moves init earlier,
> contradicting theory #1.
> 4. Just disabling the adv7482 (which registers 11 dummies i2c slaves)
> in DTS does not fix the issue.
>
> Unfortunately i2c4 is exposed on a 60-pin Samtec QSH connector only,
> for which I have no breakout adapter.

Some soldering fixed that. Still investigating.
Here's a status update:

A. I can reproduce the issue at 100 kHz instead of 400 kHz.
B. 3 above doesn't seem to be true: I can reproduce it with all other
slaves disabled.
C. The code says:

/*
* need a delay here to make register configuration
* stabilize. 1 msec at least, from empirical testing.
*/
usleep_range(1000, 2000);

However, the datasheet says:

Parameter MIN TYP MAX
Conversion Time - 2 ms -

So 1 ms is definitely too short.
Unfortunately the datasheet has no maximum value.

D. For 2: msleep(1) is sufficient, usleep_range(200, 500) is not.
And this is still not explained by C.
I also don't know yet who's resetting the chip on reboot, as it
does not have a reset line, but all registers are zeroed (except
for the POR temperature value).

To be investigated more...