ARM: tegra: Fix suspend hang on Tegra124 Chromebooks

Enabling CPUFreq support for Tegra124 Chromebooks is causing the Tegra124 to hang when resuming from suspend.

When CPUFreq is enabled, the CPU clock is changed from the PLLX clock to the DFLL clock during kernel boot. When resuming from suspend the CPU clock is temporarily changed back to the PLLX clock before switching back to the DFLL. If the DFLL is operating at a much lower frequency than the PLLX when we enter suspend, and so the CPU voltage rail is at a voltage too low for the CPUs to operate at the PLLX frequency, then the device will hang.

Please note that the PLLX is used in the resume sequence to switch the CPU clock from the very slow 32K clock to a faster clock during early resume to speed up the resume sequence before the DFLL is resumed.

Ideally, we should fix this by setting the suspend frequency so that it matches the PLLX frequency, however, that would be a bigger change. For now simply disable CPUFreq support for Tegra124 Chromebooks to avoid the hang when resuming from suspend.

Fixes 9a0baee960a7 ("ARM: tegra: Enable CPUFreq support for Tegra124

Chromebooks")

Signed-off-by Jon Hunter <[email protected]>

---

Please note that this fix is required for v4.4

 arch/arm/boot/dts/tegra124-nyan.dtsi | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

arch/arm/boot/dts/tegra124-nyan.dtsi +1 -1

index 40c23a0b7cfc..ec1aa64ded68 100644
@@ -399,7 +399,7 @@
 
 	/* CPU DFLL clock */
 	clock at 0,70110000 {
-		status = "okay";
+		status = "disabled";
 		vdd-cpu-supply = <&vdd_cpu>;
 		nvidia,i2c-fs-rate = <400000>;
 	};

Enabling CPUFreq support for Tegra124 Chromebooks is causing the Tegra124 to hang when resuming from suspend.

When CPUFreq is enabled, the CPU clock is changed from the PLLX clock to the DFLL clock during kernel boot. When resuming from suspend the CPU clock is temporarily changed back to the PLLX clock before switching back to the DFLL. If the DFLL is operating at a much lower frequency than the PLLX when we enter suspend, and so the CPU voltage rail is at a voltage too low for the CPUs to operate at the PLLX frequency, then the device will hang.

Please note that the PLLX is used in the resume sequence to switch the CPU clock from the very slow 32K clock to a faster clock during early resume to speed up the resume sequence before the DFLL is resumed.

Ideally, we should fix this by setting the suspend frequency so that it matches the PLLX frequency, however, that would be a bigger change. For now simply disable CPUFreq support for Tegra124 Chromebooks to avoid the hang when resuming from suspend.

Fixes 9a0baee960a7 ("ARM: tegra: Enable CPUFreq support for Tegra124

Chromebooks")

Signed-off-by Jon Hunter <[email protected]>

---

Please note that this fix is required for v4.4

Quoted 23 lines · Jon Hunter

Enabling CPUFreq support for Tegra124 Chromebooks is causing the Tegra124 to hang when resuming from suspend.

When CPUFreq is enabled, the CPU clock is changed from the PLLX clock to the DFLL clock during kernel boot. When resuming from suspend the CPU clock is temporarily changed back to the PLLX clock before switching back to the DFLL. If the DFLL is operating at a much lower frequency than the PLLX when we enter suspend, and so the CPU voltage rail is at a voltage too low for the CPUs to operate at the PLLX frequency, then the device will hang.

Please note that the PLLX is used in the resume sequence to switch the CPU clock from the very slow 32K clock to a faster clock during early resume to speed up the resume sequence before the DFLL is resumed.

Ideally, we should fix this by setting the suspend frequency so that it matches the PLLX frequency, however, that would be a bigger change. For now simply disable CPUFreq support for Tegra124 Chromebooks to avoid the hang when resuming from suspend.

Fixes 9a0baee960a7 ("ARM: tegra: Enable CPUFreq support for Tegra124

Chromebooks")

Quoted 4 lines

Signed-off-by Jon Hunter <[email protected]>

---

Please note that this fix is required for v4.4

Since I saw this mentioned on IRC, I applied it directly to the arm-soc fixes branch.