linux-kernel - Re: [PATCH RFC 05/14] dt-bindings/interrupt-controller: pdc: add SPI config register

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Date:   Thu, 05 Sep 2019 17:03:18 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Lina Iyer <ilina@...eaurora.org>,
        Marc Zyngier <marc.zyngier@....com>
Cc:     Rob Herring <robh@...nel.org>, evgreen@...omium.org,
        linus.walleij@...aro.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, bjorn.andersson@...aro.org,
        mkshah@...eaurora.org, linux-gpio@...r.kernel.org,
        rnayak@...eaurora.org, devicetree@...r.kernel.org
Subject: Re: [PATCH RFC 05/14] dt-bindings/interrupt-controller: pdc: add SPI config register

Quoting Lina Iyer (2019-09-03 10:07:22)
> On Mon, Sep 02 2019 at 07:58 -0600, Marc Zyngier wrote:
> >On 02/09/2019 14:38, Rob Herring wrote:
> >> On Thu, Aug 29, 2019 at 12:11:54PM -0600, Lina Iyer wrote:
> >>> In addition to configuring the PDC, additional registers that interface
> >>> the GIC have to be configured to match the GPIO type. The registers on
> >>> some QCOM SoCs are access restricted, while on other SoCs are not. They
> >>> SoCs with access restriction to these SPI registers need to be written
> >>
> >> Took me a minute to figure out this is GIC SPI interrupts, not SPI bus.
> >>
> >>> from the firmware using the SCM interface. Add a flag to indicate if the
> >>> register is to be written using SCM interface.
> >>>
> >>> Cc: devicetree@...r.kernel.org
> >>> Signed-off-by: Lina Iyer <ilina@...eaurora.org>
> >>> ---
> >>>  .../bindings/interrupt-controller/qcom,pdc.txt           | 9 ++++++++-
> >>>  1 file changed, 8 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/interrupt-controller/qcom,pdc.txt b/Documentation/devicetree/bindings/interrupt-controller/qcom,pdc.txt
> >>> index 8e0797cb1487..852fcba98ea6 100644
> >>> --- a/Documentation/devicetree/bindings/interrupt-controller/qcom,pdc.txt
> >>> +++ b/Documentation/devicetree/bindings/interrupt-controller/qcom,pdc.txt
> >>> @@ -50,15 +50,22 @@ Properties:
> >>>                 The second element is the GIC hwirq number for the PDC port.
> >>>                 The third element is the number of interrupts in sequence.
> >>>
> >>> +- qcom,scm-spi-cfg:
> >>> +   Usage: optional
> >>> +   Value type: <bool>
> >>> +   Definition: Specifies if the SPI configuration registers have to be
> >>> +               written from the firmware.
> >>> +
> >>>  Example:
> >>>
> >>>     pdc: interrupt-controller@...0000 {
> >>>             compatible = "qcom,sdm845-pdc";
> >>> -           reg = <0xb220000 0x30000>;
> >>> +           reg = <0xb220000 0x30000>, <0x179900f0 0x60>;
> >>
> >> There needs to be a description for reg updated. These aren't GIC
> >> registers are they? Because those go in the GIC node.
> >
> They are not GIC registers. I will update this documentation.
> 
> >This is completely insane. Why are the GIC registers configured as
> >secure the first place, if they are expected to be in control of the
> >non-secure?
> These are not GIC registers but located on the PDC interface to the GIC.
> They may or may not be secure access controlled, depending on the SoC.
> 

It looks like it falls under this "mailbox" device which is really the
catch all bucket for bits with no home besides they're related to the
apps CPUs/subsystem.

	apss_shared: mailbox@...90000 {
		compatible = "qcom,sdm845-apss-shared";
		reg = <0 0x17990000 0 0x1000>;
		#mbox-cells = <1>;
	};

Can you point to this node with a phandle and then parse the reg
property out of it to use in the scm readl/writel APIs? Maybe it can be
a two cell property with <&apps_shared 0xf0> to indicate the offset to
the registers to read/write? In non-secure mode presumably we need to
also write these registers? Good news is that there's a regmap for this
driver already, so maybe that can be acquired from the pdc driver.