Re: [RFC PATCH 1/1] pinctrl: rockchip: add support for per-pinmux io-domain dependency
From: Quentin Schulz
Date: Tue Feb 21 2023 - 07:15:52 EST
Hi Sascha,
On 2/15/23 11:23, Sascha Hauer wrote:
Hi Quentin,
On Tue, Aug 02, 2022 at 11:52:52AM +0200, Quentin Schulz wrote:
From: Quentin Schulz <quentin.schulz@xxxxxxxxxxxxxxxxxxxxx>
On some Rockchip SoCs, some SoC pins are split in what are called IO
domains.
An IO domain is supplied power externally, by regulators from a PMIC for
example. This external power supply is then used by the IO domain as
"supply" for the IO pins if they are outputs.
Each IO domain can configure which voltage the IO pins will be operating
on (1.8V or 3.3V).
There already exists an IO domain driver for Rockchip SoCs[1]. This
driver allows to explicit the relationship between the external power
supplies and IO domains[2]. This makes sure the regulators are enabled
by the Linux kernel so the IO domains are supplied with power and
correctly configured as per the supplied voltage.
This driver is a regulator consumer and does not offer any other
interface for device dependency.
However, IO pins belonging to an IO domain need to have this IO domain
correctly configured before they are being used otherwise they do not
operate correctly (in our case, a pin configured as output clock was
oscillating between 0 and 150mV instead of the expected 1V8).
In order to make this dependency transparent to the consumer of those
pins and not add Rockchip-specific code to third party drivers (a camera
driver in our case), it is hooked into the pinctrl driver which is
Rockchip-specific obviously.
I don't know the status of this patch, but I haven't found anything
newer, so please point me to newer patches if the discussion has
continued somewhere else. Anyway, here are some thoughts about this
patch
No new version, a bit drowning in work but we are dependent on this
patchset for an adapter board we want to upstream so I'll have to get
back to it in the next few weeks/months.
I think the general approach is fine but could be improved. Right now we
have one io-domain device with several supplies. That means once one
consumer needs an io-domain, the supplies for all domains need to be
probed beforehand. We could relax this requirement by adding a subnode
for each domain, so instead of doing this:
pmu_io_domains: io-domains {
compatible = "rockchip,rk3568-pmu-io-voltage-domain";
pmuio1-supply = <&vcc3v3_pmu>;
pmuio2-supply = <&vcc3v3_pmu>;
vccio1-supply = <&vccio_acodec>;
vccio2-supply = <&vcc_1v8>;
vccio3-supply = <&vccio_sd>;
vccio4-supply = <&vcc_1v8>;
vccio5-supply = <&vcc_3v3>;
vccio6-supply = <&vcc_1v8>;
vccio7-supply = <&vcc_3v3>;
};
We could do this:
pmu_io_domains: io-domains {
compatible = "rockchip,rk3568-pmu-io-voltage-domain";
io_domain_pmuio1: io-domain@ {
reg = <0>;
supply = <&vcc3v3_pmu>;
};
io_domain_pmuio2: io-domain@1 {
reg = <1>;
supply = <&vcc3v3_pmu>;
};
...
};
This way we could put a driver on each io-domain. When another device
needs an io-domain we no longer have to wait for all regulators to
appear, but only for the regulator that actually supplies that domain.
Mmm, that's something I indeed hadn't thought about. We'd need to handle
pmu_io_domains probing (and making available) **some** io-domains
devices and not unregister them if other io-domains devices aren't able
to probe (e.g. EPROBE_DEFER or invalid configuration for some reason;
missing supply in board DTSI). Nothing impossible, haven't developed
such a thing yet (I guess it's just kind of a bus mechanism then).
The other issue I'm thinking about ATM is whether we should support
upward compatibility (i.e. old io-domain driver with newer dts) and
backward compatibility (i.e. new io-domain driver with older dts). This
may make things a lot more complex. This is a maintainer choice though.
With that we could specify the io-domain dependencies at dtsi or core
level. A board would only have to make sure that the io-domain that is
needed to access the PMIC does not itself need a supply from the very
same PMIC to not get into circular dependencies. The supplies for the
io-domains are specified at board level anyway, so all that a board
would have to do is to skip (or replace with a fixed-regulator) the
supply for the io-domain that provides access to the I2C port the PMIC
is on. That is not too bad I guess as the regulator that supplies the
io-domain to access the PMIC needs to be always-on anyway. In the end if
we would turn that regulator off, we would no longer be able to turn it
on again.
Correct.
One thing about putting the "rockchip,io-domains" property into the
pingroups. We would have to put this property into each and every
existing pingroup in all dts[i] files and new files would have to be
reviewed in this regard as well. The pinctrl driver already has
knowledge about all pins, so I think that would be the natural place to
also add the knowledge about which io-domain a pin is in. With that in
place we would get the knowledge if a io-domain is in use and could
disable unused io-domains. I am afraid that the "rockchip,io-domains"
property would only be added in places where it actually hurts someone.
The Device Tree is here to explicit the dependencies between HW blocks,
which is what io-domains and pinctrl devices are and rockchip,io-domains
the relations between the both of them.
While we know which pin is assigned to which io-domain because it's
fixed in the silicon, this information is linking two different HW
blocks and linux drivers (and linux devices actually). I'm wondering how
exactly you think we should get this link in code without reading the
Device Tree? Because we'll have to traverse the list of io-domains
devices and find a way to identify them. This very much seems like
something DT wanted to avoid? Can you tell me what I'm missing from the
big picture?
Thanks for the feedback,
Cheers,
Quentin