On Wed, Mar 13, 2019 at 01:34:38PM +0100, Ulf Hansson wrote:
> On Mon, 11 Mar 2019 at 16:22, Adrian Bunk <bunk@xxxxxxxxxx> wrote:
> >
> > Hi,
> >
> > I am facing two issues with pwrseq_sd8787:
> >
> > 1. Usage with modular mwifiex but built-in MMC
> > I have built-in MMC (also for the root filesystem) but modular
> > pwrseq_sd8787. Are the Kconfig dependencies incorrect and I should
> > be able to set PWRSEQ_SD8787=y, or how is this supposed to work?
>
> The Kconfig currently depends on MWIFIEX, so if you have that set to M
> you can only set PWRSEQ_SD8787 to M as well.
>
> This should work!
>
> When the corresponding mmc host driver probes, the DT parsing via
> mmc_of_parse() should finds the pwrseq node, but then we fail to
> lookup the corresponding mmc pwrseq driver, simply because it has not
> been registred yet (built as module). If everything works as expected,
> this should lead to that -EPROBE_DEFER becomes propagated, such that
> the driver core re-try to prob later.
>
> Are you saying this doesn't work, no?
Not in my case, but that might be a special case:
mmc0 is using pwrseq_sd8787.
mmc1 contains the root partition where the pwrseq_sd8787 module is.
This seems to create a chicken&egg problem by also deferring detection
of the MMC root partition?
> > 2. GPIO_ACTIVE_LOW reset-gpios
> > With reset-gpios active low it is initially low,
> > mmc_pwrseq_sd8787_probe() sets that to high for a very short
> > amount of time before mmc_pwrseq_sd8787_pre_power_on() sets
> > it back to low.
> > What is the proper way to get rid of this sub-ms low-high-low?
>
> Is that not according to the spec? In such case, I suggest you post a
> patch changing the code so confirms to the spec.
>...
The spec says to keep powerdown-gpios low for at least 300ms after
enabling power.
reset-gpios controls whatever circuitry you have built for supplying
power to the chip.
Whether you make the GPIO controlling the latter active high or active
low (or not a GPIO at all) is nothing the spec cares about.
> Hope this helps!
>
> Kind regards
> Uffe
cu
Adrian
--
"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed
