Hi ARM Linux developers,
I was thinking about refactoing low level debug functions.
Before I start to write a patch, I'd like to know experts' option.
In the current implementation, "addruart" gets both
phys addr and virt addr (if CONFIG_MMU=y),
but do we really need both?
We always pick up one of them and discard the other.
Moreover, we always know which one should be used
before calling "addruart".
The idea popped up in my mind was
to split "addruart" into "addruart_phys" and "addruart_virt"
and call the only appropriate one.
The patch will change the caller in arch/arm/kernel/debug.S
as follows:
[Before]
#ifdef CONFIG_MMU
.macro addruart_current, rx, tmp1, tmp2
addruart \tmp1, \tmp2, \rx
mrc p15, 0, \rx, c1, c0
tst \rx, #1
moveq \rx, \tmp1
movne \rx, \tmp2
.endm
#else /* !CONFIG_MMU */
.macro addruart_current, rx, tmp1, tmp2
addruart \rx, \tmp1
.endm
#endif /* CONFIG_MMU */
[After]
.macro addruart_current, rx, tmp
#ifdef CONFIG_MMU
mrc p15, 0, \tmp, c1, c0
tst \tmp, #1
beq 10f
addruart_virt \rx, \tmp
b 11f
#endif
10: addruart_phys \rx, \tmp
11:
.endm
The callee in each machine (arch/arm/include/debug/*.S)
will be changed as follows:
[Before]
.macro addruart, rp, rv, tmp
ldr \rp, =CONFIG_DEBUG_UART_PHYS
ldr \rv, =CONFIG_DEBUG_UART_VIRT
.endm
[After]
.macro addruart_phys, rx, tmp
ldr \rx, =CONFIG_DEBUG_UART_PHYS
.endm
.macro addruart_virt, rx, tmp
ldr \rx, =CONFIG_DEBUG_UART_VIRT
.endm
Pros of doing this
------------------
[1] In the current implementation, the interface of addruart
is defferent depending on CONFIG_MMU.
"addruart" takes three arguments for CONFIG_MMU=y, whereas
it takes two for CONFIG_MMU is not set.
This patch will introduce the consistency of the number of
arguments.
[2] We can save one scratch register.
For example, arch/arm/boot/compressed/debug.S
gets phys addr and virt addr (r1 = phys, r2 = virt),
but r2 is not used:
ENTRY(putc)
addruart r1, r2, r3
waituart r3, r1
senduart r0, r1
busyuart r3, r1
mov pc, lr
ENDPROC(putc)
We can change this part as follows:
ENTRY(putc)
addruart_phys r1, r3
waituart r3, r1
senduart r0, r1
busyuart r3, r1
mov pc, lr
ENDPROC(putc)
If the basic idea is OK, I will take a close look.
Comments are welcome.
Best Regards
Masahiro Yamada
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