On 06/09/2023 11:19 am, Sascha Hauer wrote:
On Wed, Sep 06, 2023 at 10:20:26AM +0200, Quentin Schulz wrote:
Sascha, Robin,
On 9/5/23 11:03, Robin Murphy wrote:
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+ￜￜￜￜￜￜￜ type: boolean
+ￜￜￜￜￜￜￜ description:
+ￜￜￜￜￜￜￜￜￜ If true assume that the io domain needed for this pin
group has been
+ￜￜￜￜￜￜￜￜￜ configured correctly by the bootloader. This is needed to
break cyclic
+ￜￜￜￜￜￜￜￜￜ dependencies introduced when a io domain needs a
regulator that can be
+ￜￜￜￜￜￜￜￜￜ accessed through pins configured here.
This is describing a Linux implementation detail, not the binding
itself. There's no technical reason a DT consumer couldn't already
figure this much out from the existing topology (by observing that the
pinctrl consumer is a grandparent of the I/O domain's supply).
I am guessing you're suggesting to have some complex handling in the driver
to detect those cyclic dependencies and ignore the IO domain dependency for
the pinctrl pins where this happens?
I haven't read this as a suggestion, but only as an argument to make it
clear that I should describe the binding rather than anticipating
how it should be used.
I may have misunderstood it though.
Indeed it was more about the definition itself - an extra property isn't
*needed* to break the cycle since the cycle is already fully described
in DT, so anyone who can parse parents and phandles already has
sufficient information to detect it and break it at any point they
choose. However, as mentioned subsequently, breaking the cycle alone
isn't enough to guarantee that things will actually work in general.
AFAICS what we fundamentally need to know is the initial voltage of the
supply regulator, to be able to short-circuit requiring the I/O domain
in order to query it from the regulator itself, and instead just
initialise the I/O domain directly. However that would still represent a
bunch of fiddly extra DT parsing, so for practical purposes it seems
reasonable to then short-cut that into directly describing the initial
setting of the I/O domain on the node itself, such that the consumer of
the binding can easily handle it all in a self-contained manner.
Cheers,
Robin
One of the issues we're having here too is that we lose granularity. There
are multiple domains inside an IO domain device and here we make the whole
pinctrl device depend on all domains from one IO domain device (there can be
multiple ones) while it is factually (on the HW level) only dependent on one
domain. Considering (if I remember correctly) Heiko highly suggested we
think about adding child nodes to the IO domain devices to have a DT node
per domain in the IO domain device, how would this work with the suggested
DT binding?
I started implementing that. I have moved the IO domains into subnodes
of the IO domain controller and started adding phandles from the pin
groups in rk3568-pinctrl.dtsi to the corresponding IO domains. After a
couple of hours I had phandles for around a quarter of the existing
groups of only one SoC, so doing this for all SoCs would really be a
cumbersome job.
In the end I realized this doesn't solve any problem. Also adding the
properties I suggested doesn't prevent us from adding the more specific
dependencies from the pins to their actual IO domains later.
Sascha
