linux-kernel - [PATCH 23/24] arm64: dts: qcom: sc8280xp-crd: enable rtc

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Message-Id: <20230126142057.25715-24-johan+linaro@kernel.org>
Date:   Thu, 26 Jan 2023 15:20:56 +0100
From:   Johan Hovold <johan+linaro@...nel.org>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Bjorn Andersson <andersson@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        linux-arm-msm@...r.kernel.org, linux-rtc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Johan Hovold <johan+linaro@...nel.org>
Subject: [PATCH 23/24] arm64: dts: qcom: sc8280xp-crd: enable rtc

The SC8280XP CRD firmware does not implement the UEFI time runtime
services so the RTC in the PM8280K PMIC needs to be accessed directly.

To complicate things further, the RTC control and time registers are
read-only on this platform so an offset must be stored in some other
machine-specific non-volatile memory which an RTC driver can take into
account when reading or updating the time.

The UEFI firmware (and Windows) use a UEFI variable for this:

	882f8c2b-9646-435f-8de5-f208ff80c1bd-RTCInfo

but the offset can only be accessed via the Qualcomm UEFI Secure
Application residing in the TEE as the firmware does not implement the
variable runtime services either.

Unfortunately setting variables using this interface does not work on
the CRD so updating the time would not be possible. Instead, reserve
four bytes in one of the PMIC SDAM blocks to hold the RTC offset.

Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
---
 arch/arm64/boot/dts/qcom/sc8280xp-crd.dts | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/arm64/boot/dts/qcom/sc8280xp-crd.dts b/arch/arm64/boot/dts/qcom/sc8280xp-crd.dts
index c780b82e498d..192e076345d2 100644
--- a/arch/arm64/boot/dts/qcom/sc8280xp-crd.dts
+++ b/arch/arm64/boot/dts/qcom/sc8280xp-crd.dts
@@ -500,6 +500,21 @@ &pmk8280_pon_pwrkey {
 	status = "okay";
 };

+&pmk8280_rtc {
+	nvmem-cells = <&rtc_offset>;
+	nvmem-cell-names = "offset";
+
+	status = "okay";
+};
+
+&pmk8280_sdam_6 {
+	status = "okay";
+
+	rtc_offset: rtc-offset@bc {
+		reg = <0xbc 0x4>;
+	};
+};
+
 &qup0 {
 	status = "okay";
 };
-- 
2.39.1