[PATCH] ARM: tegra: Fix suspend hang on Tegra124 Chromebooks

[jonathanh@nvidia.com (Jon Hunter)]

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On 08/12/15 10:26, Jon Hunter wrote:
> 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 <jonathanh@nvidia.com>
> ---
> 
> 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(-)
> 
> diff --git a/arch/arm/boot/dts/tegra124-nyan.dtsi b/arch/arm/boot/dts/tegra124-nyan.dtsi
> index 40c23a0b7cfc..ec1aa64ded68 100644
> --- a/arch/arm/boot/dts/tegra124-nyan.dtsi
> +++ b/arch/arm/boot/dts/tegra124-nyan.dtsi
> @@ -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>;
>  	};
>