arm64: psci: move psci firmware calls out of line

arch/arm/kernel/psci.c +0 -8

-/*
- * The following two functions are invoked via the invoke_psci_fn pointer
- * and will not be inlined, allowing us to piggyback on the AAPCS.
- */
-static noinline int __invoke_psci_fn_hvc(u32 function_id, u32 arg0, u32 arg1,
-					 u32 arg2)
-{
-	asm volatile(

Quoted 8 lines · Will Deacon

arch/arm/kernel/psci.c +0 -8

-/*
- * The following two functions are invoked via the invoke_psci_fn pointer
- * and will not be inlined, allowing us to piggyback on the AAPCS.
- */
-static noinline int __invoke_psci_fn_hvc(u32 function_id, u32 arg0, u32 arg1,
-					 u32 arg2)
-{
-	asm volatile(

arch/arm/kernel/psci.c static u32 psci_power_state_pack(struct psci_power_state state) · line 91

Quoted 10 lines

arch/arm/kernel/psci.c +0 -10

-			__asmeq("%0", "r0")
-			__asmeq("%1", "r1")
-			__asmeq("%2", "r2")
-			__asmeq("%3", "r3")
-			__HVC(0)
-		: "+r" (function_id)
-		: "r" (arg0), "r" (arg1), "r" (arg2));
-
-	return function_id;
-}

Why not convert these to:

static int __naked __invoke_psci_fn_hvc(u32 function_id, u32 arg0, u32 arg1,

					u32 arg2)
{
	asm(
		__HVC(0)
		"bx lr");
}

?

Quoted 10 lines · Russell King - ARM Linux

Why not convert these to:

static int __naked __invoke_psci_fn_hvc(u32 function_id, u32 arg0, u32 arg1,

					u32 arg2)
{
	asm(
		__HVC(0)
		"bx lr");
}

Quoted 1 line

?

I tried this, but the compiler printed a diagnostic along the lines of "Ignoring __naked attribute", so we moved the functions out-of-line like we have on arm64 instead. Assuming it worked reliably, what's the advantage of __naked over having these out-of-line?

Quoted 11 lines · Will Deacon

Quoted 10 lines · Russell King - ARM Linux

Why not convert these to:

static int __naked __invoke_psci_fn_hvc(u32 function_id, u32 arg0, u32 arg1,

					u32 arg2)
{
	asm(
		__HVC(0)
		"bx lr");
}

Quoted 6 lines

Quoted 1 line

?

I tried this, but the compiler printed a diagnostic along the lines of "Ignoring __naked attribute", so we moved the functions out-of-line like we have on arm64 instead. Assuming it worked reliably, what's the advantage of __naked over having these out-of-line?

Note that the above isn't using any asm constraints/arguments. The GCC manual states what can be safely included:

`naked'
Use this attribute on the ARM, AVR, IP2K, RX and SPU ports to indicate that the specified function does not need prologue/epilogue sequences generated by the compiler. It is up to the programmer to provide these sequences. The only statements

that can be safely included in naked functions are `asm'

statements that do not have operands. All other statements,
^^^^^^^^^^^^^^^^^^^^^^^^^^

including declarations of local variables, `if' statements, and so forth, should be avoided. Naked functions should be used to implement the body of an assembly function, while allowing the compiler to construct the requisite function declaration for the assembler.

The advantage is that you have locality of code, and we don't need to spring up lots of assembly files along side their .c files.

I'd guess that if you try to declare local variables etc, the compiler will just ignore the naked attribute, because it then can't give the guarantees that the function will be truely naked.