[PATCH 5.5 205/367] ARM: tegra: Enable PLLP bypass during Tegra124 LP1

Greg Kroah-Hartman
2020-02-10T12:45:56Z

From: Stephen Warren <swarren@nvidia.com>

commit 1a3388d506bf5b45bb283e6a4c4706cfb4897333 upstream.

For a little over a year, U-Boot has configured the flow controller to
perform automatic RAM re-repair on off->on power transitions of the CPU
rail[1]. This is mandatory for correct operation of Tegra124. However,
RAM re-repair relies on certain clocks, which the kernel must enable and
leave running. PLLP is one of those clocks. This clock is shut down
during LP1 in order to save power. Enable bypass (which I believe routes
osc_div_clk, essentially the crystal clock, to the PLL output) so that
this clock signal toggles even though the PLL is not active. This is
required so that LP1 power mode (system suspend) operates correctly.

The bypass configuration must then be undone when resuming from LP1, so
that all peripheral clocks run at the expected rate. Without this, many
peripherals won't work correctly; for example, the UART baud rate would
be incorrect.

NVIDIA's downstream kernel code only does this if not compiled for
Tegra30, so the added code is made conditional upon the chip ID.
NVIDIA's downstream code makes this change conditional upon the active
CPU cluster. The upstream kernel currently doesn't support cluster
switching, so this patch doesn't test the active CPU cluster ID.

[1] 3cc7942a4ae5 ARM: tegra: implement RAM repair

Reported-by: Jonathan Hunter <jonathanh@nvidia.com>
Cc: stable@vger.kernel.org
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm/mach-tegra/sleep-tegra30.S | 11 +++++++++++
1 file changed, 11 insertions(+)

--- a/arch/arm/mach-tegra/sleep-tegra30.S
+++ b/arch/arm/mach-tegra/sleep-tegra30.S
@@ -370,6 +370,14 @@ _pll_m_c_x_done:
pll_locked r1, r0, CLK_RESET_PLLC_BASE
pll_locked r1, r0, CLK_RESET_PLLX_BASE

+ tegra_get_soc_id TEGRA_APB_MISC_BASE, r1
+ cmp r1, #TEGRA30
+ beq 1f
+ ldr r1, [r0, #CLK_RESET_PLLP_BASE]
+ bic r1, r1, #(1<<31) @ disable PllP bypass
+ str r1, [r0, #CLK_RESET_PLLP_BASE]
+1:
+
mov32 r7, TEGRA_TMRUS_BASE
ldr r1, [r7]
add r1, r1, #LOCK_DELAY
@@ -630,7 +638,10 @@ tegra30_switch_cpu_to_clk32k:
str r0, [r4, #PMC_PLLP_WB0_OVERRIDE]

/* disable PLLP, PLLA, PLLC and PLLX */
+ tegra_get_soc_id TEGRA_APB_MISC_BASE, r1
+ cmp r1, #TEGRA30
ldr r0, [r5, #CLK_RESET_PLLP_BASE]
+ orrne r0, r0, #(1 << 31) @ enable PllP bypass on fast cluster
bic r0, r0, #(1 << 30)
str r0, [r5, #CLK_RESET_PLLP_BASE]
ldr r0, [r5, #CLK_RESET_PLLA_BASE]