2c50a570e9
This patch was triggered by a remark from Russell that
introducing a call to the waituart (needed to fix debug prints
on the Qualcomm platforms) was dangerous because in some cases
this will involve waiting for a modem CTS (clear to send)
signal, and debug messages would maybe not work on platforms
with no modem connected to the UART port: they will just
hang waiting for the modem to assert CTS and this might never
happen.
Looking through all UART debug drivers implementing the waituart
macro I discovered that all users except two actually use this
macro to check if the UART is ready for TX, let's call this
TXRDY.
Only two debug UART drivers actually check for CTS:
- arch/arm/include/debug/8250.S
- arch/arm/include/debug/tegra.S
The former is very significant since the 8250 is possibly
the most common UART on the planet.
We have the following problem: the semantics of waituart are
ambiguous making it dangerous to introduce the macro to debug
code fixing debug prints for Qualcomm. To start to pry this
problem apart, this patch does the following:
- Convert all debug UART drivers to define two macros:
- waituartcts with the clear semantic to wait for CTS
to be asserted
- waituarttxrdy with the clear semantic to wait for the TX
capability of the UART to be ready
- When doing this take care to assign the right function to
each drivers macro, so they now do exactly the above.
- Update the three sites in the kernel invoking the waituart
macro to call waituartcts/waituarttxrdy in sequence, so that
the functional impact on the kernel should be zero.
After this we can start to change the code sites using this
code to do the right thing.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
157 lines
2.5 KiB
ArmAsm
157 lines
2.5 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* linux/arch/arm/kernel/debug.S
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*
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* Copyright (C) 1994-1999 Russell King
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*
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* 32-bit debugging code
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*/
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#include <linux/linkage.h>
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#include <asm/assembler.h>
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.text
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/*
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* Some debugging routines (useful if you've got MM problems and
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* printk isn't working). For DEBUGGING ONLY!!! Do not leave
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* references to these in a production kernel!
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*/
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#if !defined(CONFIG_DEBUG_SEMIHOSTING)
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#include CONFIG_DEBUG_LL_INCLUDE
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#endif
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#ifdef CONFIG_MMU
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.macro addruart_current, rx, tmp1, tmp2
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addruart \tmp1, \tmp2, \rx
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mrc p15, 0, \rx, c1, c0
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tst \rx, #1
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moveq \rx, \tmp1
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movne \rx, \tmp2
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.endm
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#else /* !CONFIG_MMU */
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.macro addruart_current, rx, tmp1, tmp2
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addruart \rx, \tmp1, \tmp2
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.endm
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#endif /* CONFIG_MMU */
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/*
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* Useful debugging routines
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*/
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ENTRY(printhex8)
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mov r1, #8
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b printhex
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ENDPROC(printhex8)
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ENTRY(printhex4)
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mov r1, #4
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b printhex
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ENDPROC(printhex4)
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ENTRY(printhex2)
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mov r1, #2
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printhex: adr r2, hexbuf_rel
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ldr r3, [r2]
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add r2, r2, r3
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add r3, r2, r1
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mov r1, #0
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strb r1, [r3]
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1: and r1, r0, #15
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mov r0, r0, lsr #4
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cmp r1, #10
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addlt r1, r1, #'0'
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addge r1, r1, #'a' - 10
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strb r1, [r3, #-1]!
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teq r3, r2
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bne 1b
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mov r0, r2
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b printascii
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ENDPROC(printhex2)
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.pushsection .bss
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hexbuf_addr: .space 16
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.popsection
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.align
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hexbuf_rel: .long hexbuf_addr - .
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.ltorg
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#ifndef CONFIG_DEBUG_SEMIHOSTING
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ENTRY(printascii)
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addruart_current r3, r1, r2
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1: teq r0, #0
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ldrbne r1, [r0], #1
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teqne r1, #0
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reteq lr
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2: teq r1, #'\n'
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bne 3f
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mov r1, #'\r'
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waituartcts r2, r3
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waituarttxrdy r2, r3
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senduart r1, r3
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busyuart r2, r3
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mov r1, #'\n'
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3: waituartcts r2, r3
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waituarttxrdy r2, r3
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senduart r1, r3
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busyuart r2, r3
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b 1b
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ENDPROC(printascii)
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ENTRY(printch)
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addruart_current r3, r1, r2
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mov r1, r0
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mov r0, #0
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b 2b
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ENDPROC(printch)
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#ifdef CONFIG_MMU
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ENTRY(debug_ll_addr)
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addruart r2, r3, ip
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str r2, [r0]
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str r3, [r1]
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ret lr
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ENDPROC(debug_ll_addr)
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#endif
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#else
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ENTRY(printascii)
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mov r1, r0
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mov r0, #0x04 @ SYS_WRITE0
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ARM( svc #0x123456 )
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#ifdef CONFIG_CPU_V7M
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THUMB( bkpt #0xab )
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#else
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THUMB( svc #0xab )
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#endif
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ret lr
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ENDPROC(printascii)
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ENTRY(printch)
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adr r1, hexbuf_rel
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ldr r2, [r1]
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add r1, r1, r2
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strb r0, [r1]
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mov r0, #0x03 @ SYS_WRITEC
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ARM( svc #0x123456 )
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#ifdef CONFIG_CPU_V7M
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THUMB( bkpt #0xab )
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#else
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THUMB( svc #0xab )
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#endif
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ret lr
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ENDPROC(printch)
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ENTRY(debug_ll_addr)
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mov r2, #0
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str r2, [r0]
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str r2, [r1]
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ret lr
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ENDPROC(debug_ll_addr)
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#endif
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