On Sun, Nov 10, 2019 at 7:45 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > On Thu, Oct 17, 2019 at 2:55 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > On Wed, Oct 16, 2019 at 12:23 PM Jacopo Mondi <jacopo+renesas@xxxxxxxxxx> 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@xxxxxxxxx> > > > Signed-off-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx> > > > > > 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? Not true: I managed to reproduce it with a modular driver. > > 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. usleep_range(1000, 2000) usually results in a sleep time of 2.0 ms: OK It may take longer: I saw 4.8 -- 7.7 ms (nothing in between 2.0 -- 4.8!): OK It may take shorter: - 1.2 -- 1.7 ms: FAIL - 1.8 ms - 2 ms: OK So a minimum delay of 2 ms seems like a good value. > D. For 2: msleep(1) is sufficient, usleep_range(200, 500) is not. > And this is still not explained by C. Without adding an msleep() call to max9611_init(), the usleep_range() call in max9611_read_single() happens at an arbitrary moment. After adding an msleep() call to max9611_init(), the code becomes synchronized to the jiffies clock, and the usleep_range() call in max9611_read_single() never completes in less than 2 ms, thus avoiding the issue. > 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). Looks like the PMIC powers down the +3.3V rail for ca. 25 ms when PSCI initiates a system reboot. Patch sent: "[PATCH] iio: adc: max9611: Fix too short conversion time delay" (https://lore.kernel.org/lkml/20191113092133.23723-1-geert+renesas@xxxxxxxxx/). Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
