Re: [PATCH v2 1/1] arm64: dts: ti: k3-am62-wakeup: Configure ti-sysc for wkup_uart0

From: Tony Lindgren <tony@atomide.com>
To: Kevin Hilman <khilman@kernel.org>
Cc: Nishanth Menon <nm@ti.com>, Vignesh Raghavendra <vigneshr@ti.com>,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	Dhruva Gole <d-gole@ti.com>
Subject: Re: [PATCH v2 1/1] arm64: dts: ti: k3-am62-wakeup: Configure ti-sysc for wkup_uart0
Date: Sat, 9 Dec 2023 05:59:00 +0200	[thread overview]
Message-ID: <20231209035900.GW5169@atomide.com> (raw)
In-Reply-To: <7hedfwd3co.fsf@baylibre.com>

* Kevin Hilman <khilman@kernel.org> [231208 17:13]:
> Tony Lindgren <tony@atomide.com> writes:
> 
> > * Kevin Hilman <khilman@kernel.org> [231205 18:14]:
> >> I'm a little confused why these power-domain and clocks stay here and
> >> are not moved under the wkup_uart0 node... 
> >
> > The resources are also needed by the interconnect target module. It's the
> > wrapper IP for the child device(s). In this case there's one chip 8250 IP
> > instance. In some other devices there can be multiple child IP devices
> > wired to one target module.
> >
> >> > -		clock-names = "fclk";
> >> > -		status = "disabled";
> >> > +		clock-names = "fck";
> >> > +		#address-cells = <1>;
> >> > +		#size-cells = <1>;
> >> > +		ranges = <0 0 0x2b300000 0x100000>;
> >> > +
> >> > +		wkup_uart0: serial@2b300000 {
> >> > +			compatible = "ti,am64-uart", "ti,am654-uart";
> >> > +			reg = <0 0x100>;
> >> > +			interrupts = <GIC_SPI 186 IRQ_TYPE_LEVEL_HIGH>;
> >> > +			status = "disabled";
> >> 
> >> ...here.
> >> 
> >> The SCI device ID 114 is specifically for wkup_uart0[1], so it seems to
> >> me those should be in the wkup_uart0 node.
> >
> > Those resources are also needed for the parent target module for revision
> > detection, quirks, reset, idle register configuration, and to probe the
> > child devices.
> >
> > Here the 8250 IP can be set to status = "reserved" when used by the
> > firmware, and 8250 not touched by Linux. However, the parent interconnect
> > target module still needs to be configured for idle registers and wake-up
> > path register bit so the wake-up from deeper suspend states works.
> 
> OK, makes sense.  Thanks for the clarification.

One more thing to clarify, there's nothing stopping also mapping the needed
resources for the child IP too if needed by the driver or the dts binding.
The calls for resources by the 8250 driver just won't do anything as the
resources are already enabled by the parent.

> In that case, shouldn't the same be done for the other wakeup sources
> there (e.g. wkup_rtc0) ?

Yes it should be done for devices with the wake-up path wired like
wkup_rtc0.

Regards,

Tony

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