Re: [PATCH v2 2/6] iio: adc: ti-ads1298: fix power-up and clock handling

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 24 Oct 2026 20:13:31 -0300
Stephan Costa Barros <stephanbrrs8@gmail.com> wrote:

> Fix three issues with the power-up sequence and the device clock:
> 
> - The datasheet powers up the supplies first, then the clock, then
>   waits t_POR = 2^18 clock cycles (128 ms at 2.048 MHz) before the
>   reset. The driver enabled an external clock and the vref supply
>   before AVDD, reset right away, and did not wait for the 150 ms
>   start-up of the internal reference. Follow the datasheet. Probe takes
>   about 280 ms longer.
> 
> - The binding describes one optional clock and no clock-names, but the
>   driver asked for the clock named "clk". With a device tree that
>   follows the binding, the lookup fails, the optional getter returns
>   NULL, and a clock given in the device tree is never enabled, while the
>   sampling frequency is computed from the nominal 2.048 MHz. Ask for the
>   first clock of the node; a device tree with clock-names = "clk" still
>   gets the same clock.
> 
> - A command takes 4 cycles of the device clock to decode, the minimum
>   reset pulse is 2 cycles, and the reset takes 18 more. These were
>   converted with the nominal 2.048 MHz, so a command ends after a fixed
>   2 us, short of 4 cycles with an external clock below 2 MHz, which the
>   ADS129x allows down to 1.94 MHz. Convert them with the rate of the
>   clock in use. At 2.048 MHz the delays do not change.
> 
> The clock lookup was seen to fail on a Raspberry Pi 4, with a
> fixed-clock in the device tree. The power-up order was found by review
> and reproduced on an emulated device only. The decode time was found
> with an emulated device; it is not seen on hardware running at
> 2.048 MHz.
> 
> Fixes: 00ef7708fa60 ("iio: adc: ti-ads1298: Add driver")
> Signed-off-by: Stephan Costa Barros <stephanbrrs8@gmail.com>
As before, this is multiple issues so needs breaking into more
focused patches.  That may come at the cost of some code
churn but it will make them easier to review.

Jonathan