Re: [PATCH] ARM: tegra: Fix restoration of PLLM when exiting suspend
From: Jon Hunter <jonathanh@nvidia.com>
Date: 2019-12-10 14:29:24
Also in:
linux-tegra, stable
On 10/12/2019 12:09, Thierry Reding wrote:
On Tue, Dec 10, 2019 at 10:37:08AM +0000, Jon Hunter wrote:quoted
The suspend entry and exit code for 32-bit Tegra devices assumes that the PLLM (which is used to provide the clock for external memory) is always enabled on entry to suspend. Hence, the current code always disables the PLLM on entry to suspend and re-enables the PLLM on exit from suspend. Since the introduction of the Tegra124 EMC driver by commit 73a7f0a90641 ("memory: tegra: Add EMC (external memory controller) driver"), which is used to scale the EMC frequency, PLLM may not be the current clock source for the EMC on entry to suspend and hence may not be enabled. Always enabling the PLLM on exit from suspend can cause the actual status on the PLL to be different from that reported by the common clock framework. On kernels prior to v4.5, the code to set the rate of the PLLM had a test to verify if the PLL was enabled and if the PLL was enabled, setting the rate would fail. Since commit 267b62a96951 ("clk: tegra: pll: Update PLLM handling") the test to see if PLLM is enabled was removed. With these earlier kernels, if the PLLM is disabled on entering suspend and the EMC driver attempts to set the parent of the EMC clock to the PLLM on exiting suspend, then the set rate for the PLLM will fail and in turn cause the resume to fail. We should not be re-enabling the PLLM on resume from suspend unless it was enabled on entry to suspend. Therefore, fix this by saving the state of PLLM on entry to suspend and only re-enable it, if it was already enabled. Fixes: 73a7f0a90641 ("memory: tegra: Add EMC (external memory controller) driver") Cc: stable@vger.kernel.org Signed-off-by: Jon Hunter <jonathanh@nvidia.com> --- arch/arm/mach-tegra/sleep-tegra30.S | 33 +++++++++++++++++++++++------ 1 file changed, 27 insertions(+), 6 deletions(-)Looks good to me. If I understand correctly we really only need this on v4.4 and earlier because the issue doesn't happen on later kernels because of that PLLM handling update change that you mentioned, right?
Yes.
At the same time, this is the correct thing to do even on more recent kernels because we currently rely on the PLLM status check being absent for this to work.
Yes exactly.
So it seems like the safest option going forward is to apply this patch to all versions, so that we don't rely on any assumptions. Do you agree?
Yes, my feeling is that we should apply to mainline and then it should be picked-up for stable. Cheers Jon -- nvpublic _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel