[PATCH 1/2] ARM: tegra: add CPU errata WARs to Tegra reset handler

[PATCH 1/2] ARM: tegra: add CPU errata WARs to Tegra reset handler

[Stephen Warren]

From: Stephen Warren <swarren@nvidia.com>

The CPU cores in Tegra contain some errata. Workarounds must be applied
for these every time a CPU boots. Implement those workarounds directly
in the Tegra-specific CPU reset vector.

Many of these workarounds duplicate code in the core ARM kernel.

However, the core ARM kernel cannot enable those workarounds when
building a multi-platform kernel, since they require writing to secure-
only registers, and a multi-platform kernel often does not run in secure
mode, and also cannot generically/architecturally detect whether it is
running in secure mode, and hence cannot either unconditionally or
conditionally apply these workarounds.

Instead, the workarounds must be applied in architecture-specific reset
code, which is able to have more direct knowledge of the secure/normal
state. On Tegra, we will be able to detect this using a non-architected
register in the future, although we currently assume the kernel runs only
in secure mode. Other SoCs may never run the kernel in secure mode, and
hence always rely on a secure monitor to enable the workarounds, and
hence never implement them in the kernel.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
---
 arch/arm/mach-tegra/reset-handler.S |   45 ++++++++++++++++++++++++++++++-----
 1 file changed, 39 insertions(+), 6 deletions(-)

diff --git a/arch/arm/mach-tegra/reset-handler.S b/arch/arm/mach-tegra/reset-handler.S
index 54382ce..ff7b45c 100644
--- a/arch/arm/mach-tegra/reset-handler.S
+++ b/arch/arm/mach-tegra/reset-handler.S
@@ -99,6 +99,8 @@ ENTRY(__tegra_cpu_reset_handler_start)
  *
  * Register usage within the reset handler:
  *
+ *      Others: scratch
+ *      R6  = SoC ID << 8
  *      R7  = CPU present (to the OS) mask
  *      R8  = CPU in LP1 state mask
  *      R9  = CPU in LP2 state mask
@@ -114,6 +116,40 @@ ENTRY(__tegra_cpu_reset_handler_start)
 ENTRY(__tegra_cpu_reset_handler)
 
 	cpsid	aif, 0x13			@ SVC mode, interrupts disabled
+
+	mov32	r6, TEGRA_APB_MISC_BASE
+	ldr	r6, [r6, #APB_MISC_GP_HIDREV]
+	and	r6, r6, #0xff00
+#ifdef CONFIG_ARCH_TEGRA_2x_SOC
+t20_check:
+	cmp	r6, #(0x20 << 8)
+	bne	after_t20_check
+t20_errata:
+	# Tegra20 is a Cortex-A9 r1p1
+	mrc	p15, 0, r0, c1, c0, 0   @ read system control register
+	orr	r0, r0, #1 << 14        @ erratum 716044
+	mcr	p15, 0, r0, c1, c0, 0   @ write system control register
+	mrc	p15, 0, r0, c15, c0, 1  @ read diagnostic register
+	orr	r0, r0, #1 << 4         @ erratum 742230
+	orr	r0, r0, #1 << 11        @ erratum 751472
+	mcr	p15, 0, r0, c15, c0, 1  @ write diagnostic register
+	b	after_errata
+after_t20_check:
+#endif
+#ifdef CONFIG_ARCH_TEGRA_3x_SOC
+t30_check:
+	cmp	r6, #(0x30 << 8)
+	bne	after_t30_check
+t30_errata:
+	# Tegra30 is a Cortex-A9 r2p9
+	mrc	p15, 0, r0, c15, c0, 1  @ read diagnostic register
+	orr	r0, r0, #1 << 6         @ erratum 743622
+	orr	r0, r0, #1 << 11        @ erratum 751472
+	mcr	p15, 0, r0, c15, c0, 1  @ write diagnostic register
+	b	after_errata
+after_t30_check:
+#endif
+after_errata:
 	mrc	p15, 0, r10, c0, c0, 5		@ MPIDR
 	and	r10, r10, #0x3			@ R10 = CPU number
 	mov	r11, #1
@@ -129,16 +165,13 @@ ENTRY(__tegra_cpu_reset_handler)
 
 #ifdef CONFIG_ARCH_TEGRA_2x_SOC
 	/* Are we on Tegra20? */
-	mov32	r6, TEGRA_APB_MISC_BASE
-	ldr	r0, [r6, #APB_MISC_GP_HIDREV]
-	and	r0, r0, #0xff00
-	cmp	r0, #(0x20 << 8)
+	cmp	r6, #(0x20 << 8)
 	bne	1f
 	/* If not CPU0, don't let CPU0 reset CPU1 now that CPU1 is coming up. */
-	mov32	r6, TEGRA_PMC_BASE
+	mov32	r5, TEGRA_PMC_BASE
 	mov	r0, #0
 	cmp	r10, #0
-	strne	r0, [r6, #PMC_SCRATCH41]
+	strne	r0, [r5, #PMC_SCRATCH41]
 1:
 #endif
 
-- 
1.7.10.4

[PATCH 2/2] ARM: tegra: remove save/restore of CPU diag register

[Stephen Warren]

From: Stephen Warren <swarren@nvidia.com>

Prior to this change, {save,restore}_cpu_arch_register() collaborated to
maintain the value of the CPU diagnostic register across power cycles.
This was required to maintain any CPU errata workaround enable bits in
that register. However, now that the Tegra reset vector code always
enables all required workarounds, there is no need to save and restore
the diagnostic register; it is always explicitly programmed in the
required manner.

Hence, remove the save/restore logic.

This has the advantage that the kernel always directly controls the value
of this register every boot, rather than relying on a bootloader or other
kernel code having previously written the correct value into it. This
makes CPU0 (which was previously saved/restored) and CPUn (which should
have been set up by the reset vector) be controlled in exactly the same
way, which is easier to debug/find/...

In particular, when converting Tegra to a multi-platform kernel, the CPU0
diagnostic register value initially comes from the bootloader. Most Tegra
bootloaders don't yet enable all required CPU bug workarounds. The
previous commit updates the kernel to do so on any CPU power cycle.
However, the save/restore code ends up over-writing the value with the
old bootloader-driven value instead of the now more-likely-to-be-correct
kernel value!

Even irrespective of multi-platform conversion, this change limits the
kernel's exposure to any WARs the bootloader didn't enable for CPU0: on
the very first LP2 transition (CPU power-saving which power-cycles the
CPU), the correct value will be enabled.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
---
 arch/arm/mach-tegra/cpuidle-tegra30.c |    4 ----
 arch/arm/mach-tegra/pm.c              |   19 -------------------
 2 files changed, 23 deletions(-)

diff --git a/arch/arm/mach-tegra/cpuidle-tegra30.c b/arch/arm/mach-tegra/cpuidle-tegra30.c
index 8b50cf4..80445ed 100644
--- a/arch/arm/mach-tegra/cpuidle-tegra30.c
+++ b/arch/arm/mach-tegra/cpuidle-tegra30.c
@@ -102,12 +102,8 @@ static bool tegra30_cpu_core_power_down(struct cpuidle_device *dev,
 
 	smp_wmb();
 
-	save_cpu_arch_register();
-
 	cpu_suspend(0, tegra30_sleep_cpu_secondary_finish);
 
-	restore_cpu_arch_register();
-
 	clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
 
 	return true;
diff --git a/arch/arm/mach-tegra/pm.c b/arch/arm/mach-tegra/pm.c
index 523604d..0494f73 100644
--- a/arch/arm/mach-tegra/pm.c
+++ b/arch/arm/mach-tegra/pm.c
@@ -46,26 +46,11 @@
 #define PMC_CPUPWROFF_TIMER	0xcc
 
 #ifdef CONFIG_PM_SLEEP
-static unsigned int g_diag_reg;
 static DEFINE_SPINLOCK(tegra_lp2_lock);
 static void __iomem *pmc = IO_ADDRESS(TEGRA_PMC_BASE);
 static struct clk *tegra_pclk;
 void (*tegra_tear_down_cpu)(void);
 
-void save_cpu_arch_register(void)
-{
-	/* read diagnostic register */
-	asm("mrc p15, 0, %0, c15, c0, 1" : "=r"(g_diag_reg) : : "cc");
-	return;
-}
-
-void restore_cpu_arch_register(void)
-{
-	/* write diagnostic register */
-	asm("mcr p15, 0, %0, c15, c0, 1" : : "r"(g_diag_reg) : "cc");
-	return;
-}
-
 static void set_power_timers(unsigned long us_on, unsigned long us_off)
 {
 	unsigned long long ticks;
@@ -119,8 +104,6 @@ static void restore_cpu_complex(void)
 	tegra_cpu_clock_resume();
 
 	flowctrl_cpu_suspend_exit(cpu);
-
-	restore_cpu_arch_register();
 }
 
 /*
@@ -145,8 +128,6 @@ static void suspend_cpu_complex(void)
 	tegra_cpu_clock_suspend();
 
 	flowctrl_cpu_suspend_enter(cpu);
-
-	save_cpu_arch_register();
 }
 
 void tegra_clear_cpu_in_lp2(int phy_cpu_id)
-- 
1.7.10.4

[PATCH 1/2] ARM: tegra: add CPU errata WARs to Tegra reset handler

[Stephen Warren]

On 03/04/2013 05:05 PM, Stephen Warren wrote:
> The CPU cores in Tegra contain some errata. Workarounds must be applied
> for these every time a CPU boots. Implement those workarounds directly
> in the Tegra-specific CPU reset vector.
> 
> Many of these workarounds duplicate code in the core ARM kernel.
> 
> However, the core ARM kernel cannot enable those workarounds when
> building a multi-platform kernel, since they require writing to secure-
> only registers, and a multi-platform kernel often does not run in secure
> mode, and also cannot generically/architecturally detect whether it is
> running in secure mode, and hence cannot either unconditionally or
> conditionally apply these workarounds.
> 
> Instead, the workarounds must be applied in architecture-specific reset
> code, which is able to have more direct knowledge of the secure/normal
> state. On Tegra, we will be able to detect this using a non-architected
> register in the future, although we currently assume the kernel runs only
> in secure mode. Other SoCs may never run the kernel in secure mode, and
> hence always rely on a secure monitor to enable the workarounds, and
> hence never implement them in the kernel.

I have applied this series to Tegra's for-3.10/fixes branch.