forked from luck/tmp_suning_uos_patched
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>
45 lines
896 B
ArmAsm
45 lines
896 B
ArmAsm
/* SPDX-License-Identifier: GPL-2.0-only */
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/* arch/arm/include/debug/pl01x.S
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*
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* Debugging macro include header
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*
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* Copyright (C) 1994-1999 Russell King
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* Moved from linux/arch/arm/kernel/debug.S by Ben Dooks
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*/
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#include <linux/amba/serial.h>
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#ifdef CONFIG_DEBUG_ZTE_ZX
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#undef UART01x_DR
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#undef UART01x_FR
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#define UART01x_DR 0x04
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#define UART01x_FR 0x14
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#endif
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#ifdef CONFIG_DEBUG_UART_PHYS
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.macro addruart, rp, rv, tmp
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ldr \rp, =CONFIG_DEBUG_UART_PHYS
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ldr \rv, =CONFIG_DEBUG_UART_VIRT
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.endm
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#endif
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.macro senduart,rd,rx
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strb \rd, [\rx, #UART01x_DR]
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.endm
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.macro waituartcts,rd,rx
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.endm
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.macro waituarttxrdy,rd,rx
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1001: ldr \rd, [\rx, #UART01x_FR]
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ARM_BE8( rev \rd, \rd )
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tst \rd, #UART01x_FR_TXFF
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bne 1001b
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.endm
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.macro busyuart,rd,rx
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1001: ldr \rd, [\rx, #UART01x_FR]
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ARM_BE8( rev \rd, \rd )
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tst \rd, #UART01x_FR_BUSY
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bne 1001b
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.endm
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