[PATCH 3.14 66/77] arm64: kernel: refactor the CPU suspend API for retention states
3.14-stable review patch. If anyone has any objections, please let me know.
--
From: Lorenzo Pieralisi
commit 714f59925595b9c2ea9c22b107b340d38e3b3bc9 upstream.
CPU suspend is the standard kernel interface to be used to enter
low-power states on ARM64 systems. Current cpu_suspend implementation
by default assumes that all low power states are losing the CPU context,
so the CPU registers must be saved and cleaned to DRAM upon state
entry. Furthermore, the current cpu_suspend() implementation assumes
that if the CPU suspend back-end method returns when called, this has
to be considered an error regardless of the return code (which can be
successful) since the CPU was not expected to return from a code path that
is different from cpu_resume code path - eg returning from the reset vector.
All in all this means that the current API does not cope well with low-power
states that preserve the CPU context when entered (ie retention states),
since first of all the context is saved for nothing on state entry for
those states and a successful state entry can return as a normal function
return, which is considered an error by the current CPU suspend
implementation.
This patch refactors the cpu_suspend() API so that it can be split in
two separate functionalities. The arm64 cpu_suspend API just provides
a wrapper around CPU suspend operation hook. A new function is
introduced (for architecture code use only) for states that require
context saving upon entry:
__cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
__cpu_suspend() saves the context on function entry and calls the
so called suspend finisher (ie fn) to complete the suspend operation.
The finisher is not expected to return, unless it fails in which case
the error is propagated back to the __cpu_suspend caller.
The API refactoring results in the following pseudo code call sequence for a
suspending CPU, when triggered from a kernel subsystem:
/*
* int cpu_suspend(unsigned long idx)
* @idx: idle state index
*/
{
-> cpu_suspend(idx)
|---> CPU operations suspend hook called, if present
|--> if (retention_state)
|--> direct suspend back-end call (eg PSCI suspend)
else
|--> __cpu_suspend(idx, _end_finisher);
}
By refactoring the cpu_suspend API this way, the CPU operations back-end
has a chance to detect whether idle states require state saving or not
and can call the required suspend operations accordingly either through
simple function call or indirectly through __cpu_suspend() which carries out
state saving and suspend finisher dispatching to complete idle state entry.
Reviewed-by: Catalin Marinas
Reviewed-by: Hanjun Guo
Signed-off-by: Lorenzo Pieralisi
Signed-off-by: Catalin Marinas
Signed-off-by: Greg Kroah-Hartman
---
arch/arm64/include/asm/suspend.h |1
arch/arm64/kernel/sleep.S| 47 +++---
arch/arm64/kernel/suspend.c | 48 +++
3 files changed, 64 insertions(+), 32 deletions(-)
--- a/arch/arm64/include/asm/suspend.h
+++ b/arch/arm64/include/asm/suspend.h
@@ -21,6 +21,7 @@ struct sleep_save_sp {
phys_addr_t save_ptr_stash_phys;
};
+extern int __cpu_suspend(unsigned long arg, int (*fn)(unsigned long));
extern void cpu_resume(void);
extern int cpu_suspend(unsigned long);
--- a/arch/arm64/kernel/sleep.S
+++ b/arch/arm64/kernel/sleep.S
@@ -49,28 +49,39 @@
orr \dst, \dst, \mask // dst|=(aff3>>rs3)
.endm
/*
- * Save CPU state for a suspend. This saves callee registers, and allocates
- * space on the kernel stack to save the CPU specific registers + some
- * other data for resume.
+ * Save CPU state for a suspend and execute the suspend finisher.
+ * On success it will return 0 through cpu_resume - ie through a CPU
+ * soft/hard reboot from the reset vector.
+ * On failure it returns the suspend finisher return value or force
+ * -EOPNOTSUPP if the finisher erroneously returns 0 (the suspend finisher
+ * is not allowed to return, if it does this must be considered failure).
+ * It saves callee registers, and allocates space on the kernel stack
+ * to save the CPU specific registers + some other data for resume.
*
* x0 = suspend finisher argument
+ * x1 = suspend finisher function pointer
*/
-ENTRY(__cpu_suspend)
+ENTRY(__cpu_suspend_enter)
stp x29, lr, [sp, #-96]!
stp x19, x20, [sp,#16]
stp x21, x22, [sp,#32]
stp x23, x24, [sp,#48]
stp x25, x26, [sp,#64]
stp x27, x28, [sp,#80]
+ /*
+* Stash suspend finisher and its argument in x20 and x19
+*/
+ mov x19, x0
+ mov x20, x1
mov x2, sp
sub sp, sp, #CPU_SUSPEND_SZ // allocate cpu_suspend_ctx
- mov x1, sp
+ mov x0, sp
/*
-* x1 now points to struct cpu_suspend_ctx
[PATCH 3.14 66/77] arm64: kernel: refactor the CPU suspend API for retention states
3.14-stable review patch. If anyone has any objections, please let me know.
--
From: Lorenzo Pieralisi lorenzo.pieral...@arm.com
commit 714f59925595b9c2ea9c22b107b340d38e3b3bc9 upstream.
CPU suspend is the standard kernel interface to be used to enter
low-power states on ARM64 systems. Current cpu_suspend implementation
by default assumes that all low power states are losing the CPU context,
so the CPU registers must be saved and cleaned to DRAM upon state
entry. Furthermore, the current cpu_suspend() implementation assumes
that if the CPU suspend back-end method returns when called, this has
to be considered an error regardless of the return code (which can be
successful) since the CPU was not expected to return from a code path that
is different from cpu_resume code path - eg returning from the reset vector.
All in all this means that the current API does not cope well with low-power
states that preserve the CPU context when entered (ie retention states),
since first of all the context is saved for nothing on state entry for
those states and a successful state entry can return as a normal function
return, which is considered an error by the current CPU suspend
implementation.
This patch refactors the cpu_suspend() API so that it can be split in
two separate functionalities. The arm64 cpu_suspend API just provides
a wrapper around CPU suspend operation hook. A new function is
introduced (for architecture code use only) for states that require
context saving upon entry:
__cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
__cpu_suspend() saves the context on function entry and calls the
so called suspend finisher (ie fn) to complete the suspend operation.
The finisher is not expected to return, unless it fails in which case
the error is propagated back to the __cpu_suspend caller.
The API refactoring results in the following pseudo code call sequence for a
suspending CPU, when triggered from a kernel subsystem:
/*
* int cpu_suspend(unsigned long idx)
* @idx: idle state index
*/
{
- cpu_suspend(idx)
|--- CPU operations suspend hook called, if present
|-- if (retention_state)
|-- direct suspend back-end call (eg PSCI suspend)
else
|-- __cpu_suspend(idx, back_end_finisher);
}
By refactoring the cpu_suspend API this way, the CPU operations back-end
has a chance to detect whether idle states require state saving or not
and can call the required suspend operations accordingly either through
simple function call or indirectly through __cpu_suspend() which carries out
state saving and suspend finisher dispatching to complete idle state entry.
Reviewed-by: Catalin Marinas catalin.mari...@arm.com
Reviewed-by: Hanjun Guo hanjun@linaro.org
Signed-off-by: Lorenzo Pieralisi lorenzo.pieral...@arm.com
Signed-off-by: Catalin Marinas catalin.mari...@arm.com
Signed-off-by: Greg Kroah-Hartman gre...@linuxfoundation.org
---
arch/arm64/include/asm/suspend.h |1
arch/arm64/kernel/sleep.S| 47 +++---
arch/arm64/kernel/suspend.c | 48 +++
3 files changed, 64 insertions(+), 32 deletions(-)
--- a/arch/arm64/include/asm/suspend.h
+++ b/arch/arm64/include/asm/suspend.h
@@ -21,6 +21,7 @@ struct sleep_save_sp {
phys_addr_t save_ptr_stash_phys;
};
+extern int __cpu_suspend(unsigned long arg, int (*fn)(unsigned long));
extern void cpu_resume(void);
extern int cpu_suspend(unsigned long);
--- a/arch/arm64/kernel/sleep.S
+++ b/arch/arm64/kernel/sleep.S
@@ -49,28 +49,39 @@
orr \dst, \dst, \mask // dst|=(aff3rs3)
.endm
/*
- * Save CPU state for a suspend. This saves callee registers, and allocates
- * space on the kernel stack to save the CPU specific registers + some
- * other data for resume.
+ * Save CPU state for a suspend and execute the suspend finisher.
+ * On success it will return 0 through cpu_resume - ie through a CPU
+ * soft/hard reboot from the reset vector.
+ * On failure it returns the suspend finisher return value or force
+ * -EOPNOTSUPP if the finisher erroneously returns 0 (the suspend finisher
+ * is not allowed to return, if it does this must be considered failure).
+ * It saves callee registers, and allocates space on the kernel stack
+ * to save the CPU specific registers + some other data for resume.
*
* x0 = suspend finisher argument
+ * x1 = suspend finisher function pointer
*/
-ENTRY(__cpu_suspend)
+ENTRY(__cpu_suspend_enter)
stp x29, lr, [sp, #-96]!
stp x19, x20, [sp,#16]
stp x21, x22, [sp,#32]
stp x23, x24, [sp,#48]
stp x25, x26, [sp,#64]
stp x27, x28, [sp,#80]
+ /*
+* Stash suspend finisher and its argument in x20 and x19
+*/
+ mov x19, x0
+ mov x20, x1
mov x2, sp
sub sp, sp, #CPU_SUSPEND_SZ //
