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

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

[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")

Signed-off-by: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
---

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@0,70110000 {
-		status = "okay";
+		status = "disabled";
 		vdd-cpu-supply = <&vdd_cpu>;
 		nvidia,i2c-fs-rate = <400000>;
 	};
-- 
2.1.4

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

[Jon Hunter]

Ping?

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-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
> ---
> 
> 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@0,70110000 {
> -		status = "okay";
> +		status = "disabled";
>  		vdd-cpu-supply = <&vdd_cpu>;
>  		nvidia,i2c-fs-rate = <400000>;
>  	};
> 
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Re: [PATCH] ARM: tegra: Fix suspend hang on Tegra124 Chromebooks

[Olof Johansson]

On Tue, Dec 08, 2015 at 10:26:49AM +0000, 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-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
> ---
> 
> 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.


Thanks,

-Olof

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

[Jon Hunter]

On 22/12/15 23:42, Olof Johansson wrote:
> On Tue, Dec 08, 2015 at 10:26:49AM +0000, 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-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>> ---
>>
>> 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.

Thanks!

Cheers Jon