From 2c50a570e9dc649c182268e779dffe0712e98a6a Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Thu, 27 Aug 2020 23:25:37 +0100 Subject: ARM: 9004/1: debug: Split waituart to CTS and TXRDY 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 Signed-off-by: Russell King --- arch/arm/kernel/debug.S | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'arch/arm/kernel/debug.S') diff --git a/arch/arm/kernel/debug.S b/arch/arm/kernel/debug.S index e112072b579d..e7c87522c176 100644 --- a/arch/arm/kernel/debug.S +++ b/arch/arm/kernel/debug.S @@ -89,11 +89,13 @@ ENTRY(printascii) 2: teq r1, #'\n' bne 3f mov r1, #'\r' - waituart r2, r3 + waituartcts r2, r3 + waituarttxrdy r2, r3 senduart r1, r3 busyuart r2, r3 mov r1, #'\n' -3: waituart r2, r3 +3: waituartcts r2, r3 + waituarttxrdy r2, r3 senduart r1, r3 busyuart r2, r3 b 1b -- cgit v1.2.3 From 4df24fef09615d8f7dd2120f5072486addfd3eb9 Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Thu, 27 Aug 2020 23:28:56 +0100 Subject: ARM: 9005/1: debug: Select flow control for all debug UARTs Instead of a flow control selection mechanism specifically for 8250, make this available for all debug UARTs. If the debug UART supports waiting for CTS to be asserted, then this code can be activated for terminals that need it. We keep the defaults for EBSA110, Footbridge, Gemini and RPC so that this still works as expected for these older platforms: they assume that flow control shall be enabled for debug prints. I switch the location of the check for ifdef CONFIG_DEBUG_UART_FLOW_CONTROL from the actual debug UART drivers: the code would get compiled-out for 8250 and Tegra unless their custom config (or passing -DFLOW_CONTROL in the Tegra case) was not set. Instead this is conditional at the three places where we print debug messages. The idea is that debug UARTs can be implemented without this ifdef boilerplate so they look cleaner, alas the ifdef has to be somewhere. Signed-off-by: Linus Walleij Signed-off-by: Russell King --- arch/arm/Kconfig.debug | 16 +++++++++++----- arch/arm/boot/compressed/debug.S | 2 ++ arch/arm/include/debug/8250.S | 2 -- arch/arm/include/debug/tegra.S | 2 -- arch/arm/kernel/debug.S | 7 ++++++- 5 files changed, 19 insertions(+), 10 deletions(-) (limited to 'arch/arm/kernel/debug.S') diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug index 80000a66a4e3..87912e5c2256 100644 --- a/arch/arm/Kconfig.debug +++ b/arch/arm/Kconfig.debug @@ -1546,6 +1546,17 @@ config DEBUG_SIRFSOC_UART bool depends on ARCH_SIRF +config DEBUG_UART_FLOW_CONTROL + bool "Enable flow control (CTS) for the debug UART" + depends on DEBUG_LL + default y if ARCH_EBSA110 || DEBUG_FOOTBRIDGE_COM1 || DEBUG_GEMINI || ARCH_RPC + help + Some UART ports are connected to terminals that will use modem + control signals to indicate whether they are ready to receive text. + In practice this means that the terminal is asserting the special + control signal CTS (Clear To Send). If your debug UART supports + this and your debug terminal will require it, enable this option. + config DEBUG_LL_INCLUDE string default "debug/sa1100.S" if DEBUG_SA1100 @@ -1893,11 +1904,6 @@ config DEBUG_UART_8250_PALMCHIP except for having a different register layout. Say Y here if the debug UART is of this type. -config DEBUG_UART_8250_FLOW_CONTROL - bool "Enable flow control for 8250 UART" - depends on DEBUG_LL_UART_8250 || DEBUG_UART_8250 - default y if ARCH_EBSA110 || DEBUG_FOOTBRIDGE_COM1 || DEBUG_GEMINI || ARCH_RPC - config DEBUG_UNCOMPRESS bool "Enable decompressor debugging via DEBUG_LL output" depends on ARCH_MULTIPLATFORM || PLAT_SAMSUNG || ARM_SINGLE_ARMV7M diff --git a/arch/arm/boot/compressed/debug.S b/arch/arm/boot/compressed/debug.S index 97f4e74692e8..fac40a717fcf 100644 --- a/arch/arm/boot/compressed/debug.S +++ b/arch/arm/boot/compressed/debug.S @@ -8,7 +8,9 @@ ENTRY(putc) addruart r1, r2, r3 +#ifdef CONFIG_DEBUG_UART_FLOW_CONTROL waituartcts r3, r1 +#endif waituarttxrdy r3, r1 senduart r0, r1 busyuart r3, r1 diff --git a/arch/arm/include/debug/8250.S b/arch/arm/include/debug/8250.S index 769246d87fff..e3692a37cede 100644 --- a/arch/arm/include/debug/8250.S +++ b/arch/arm/include/debug/8250.S @@ -49,9 +49,7 @@ .endm .macro waituartcts,rd,rx -#ifdef CONFIG_DEBUG_UART_8250_FLOW_CONTROL 1001: load \rd, [\rx, #UART_MSR << UART_SHIFT] tst \rd, #UART_MSR_CTS beq 1001b -#endif .endm diff --git a/arch/arm/include/debug/tegra.S b/arch/arm/include/debug/tegra.S index 2bca6358cdd0..98daa7f48314 100644 --- a/arch/arm/include/debug/tegra.S +++ b/arch/arm/include/debug/tegra.S @@ -179,14 +179,12 @@ .endm .macro waituartcts, rd, rx -#ifdef FLOW_CONTROL cmp \rx, #0 beq 1002f 1001: ldrb \rd, [\rx, #UART_MSR << UART_SHIFT] tst \rd, #UART_MSR_CTS beq 1001b 1002: -#endif .endm .macro waituarttxrdy,rd,rx diff --git a/arch/arm/kernel/debug.S b/arch/arm/kernel/debug.S index e7c87522c176..d92f44bdf438 100644 --- a/arch/arm/kernel/debug.S +++ b/arch/arm/kernel/debug.S @@ -89,12 +89,17 @@ ENTRY(printascii) 2: teq r1, #'\n' bne 3f mov r1, #'\r' +#ifdef CONFIG_DEBUG_UART_FLOW_CONTROL waituartcts r2, r3 +#endif waituarttxrdy r2, r3 senduart r1, r3 busyuart r2, r3 mov r1, #'\n' -3: waituartcts r2, r3 +3: +#ifdef CONFIG_DEBUG_UART_FLOW_CONTROL + waituartcts r2, r3 +#endif waituarttxrdy r2, r3 senduart r1, r3 busyuart r2, r3 -- cgit v1.2.3