From 55b2b77744b457403949a6aa1aea16df2e61e70c Mon Sep 17 00:00:00 2001 From: =?utf8?q?Rafa=C5=82=20Mi=C5=82ecki?= Date: Wed, 20 Apr 2016 06:05:56 +0000 Subject: [PATCH] ar71xx: fix nondeterministic hangs during bootconsole/console handover Reconfiguring the UART when the FIFO is not empty may cause the boot to hang. This hang is extremely suspectible to timing differences; recompiling the kernel with the same configuration, but different UTS_VERSION timestamps can yield images that hang more or less often. Sometimes images are produced that hang reproducibly. This patch should also make it into one of the next linux-stable releases, but it's better to get this fixed as soon as possible. Fixes #21773, #21857. Signed-off-by: Matthias Schiffer Backport of r49156 SVN-Revision: 49202 --- ...bootconsole-wait-for-both-THRE-and-T.patch | 49 +++++++++++++++++++ ...S-ath79-enable-UART-for-early_serial.patch | 4 +- ...PS-ath79-add-support-for-QCA953x-SoC.patch | 6 +-- ...PS-ath79-add-support-for-QCA956x-SoC.patch | 6 +-- 4 files changed, 57 insertions(+), 8 deletions(-) create mode 100644 target/linux/ar71xx/patches-3.18/003-MIPS-ath79-make-bootconsole-wait-for-both-THRE-and-T.patch diff --git a/target/linux/ar71xx/patches-3.18/003-MIPS-ath79-make-bootconsole-wait-for-both-THRE-and-T.patch b/target/linux/ar71xx/patches-3.18/003-MIPS-ath79-make-bootconsole-wait-for-both-THRE-and-T.patch new file mode 100644 index 0000000000..2eba263732 --- /dev/null +++ b/target/linux/ar71xx/patches-3.18/003-MIPS-ath79-make-bootconsole-wait-for-both-THRE-and-T.patch @@ -0,0 +1,49 @@ +From f1ba020af5076172c9d29006a747ccf40027fedc Mon Sep 17 00:00:00 2001 +Message-Id: +From: Matthias Schiffer +Date: Thu, 24 Mar 2016 15:34:05 +0100 +Subject: [PATCH] MIPS: ath79: make bootconsole wait for both THRE and TEMT + +This makes the ath79 bootconsole behave the same way as the generic 8250 +bootconsole. + +Also waiting for TEMT (transmit buffer is empty) instead of just THRE +(transmit buffer is not full) ensures that all characters have been +transmitted before the real serial driver starts reconfiguring the serial +controller (which would sometimes result in garbage being transmitted.) +This change does not cause a visible performance loss. + +In addition, this seems to fix a hang observed in certain configurations on +many AR7xxx/AR9xxx SoCs during autoconfig of the real serial driver. + +A more complete follow-up patch will disable 8250 autoconfig for ath79 +altogether (the serial controller is detected as a 16550A, which is not +fully compatible with the ath79 serial, and the autoconfig may lead to +undefined behavior on ath79.) + +Cc: +Signed-off-by: Matthias Schiffer +--- + arch/mips/ath79/early_printk.c | 6 ++++-- + 1 file changed, 4 insertions(+), 2 deletions(-) + +--- a/arch/mips/ath79/early_printk.c ++++ b/arch/mips/ath79/early_printk.c +@@ -31,13 +31,15 @@ static inline void prom_putchar_wait(voi + } while (1); + } + ++#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE) ++ + static void prom_putchar_ar71xx(unsigned char ch) + { + void __iomem *base = (void __iomem *)(KSEG1ADDR(AR71XX_UART_BASE)); + +- prom_putchar_wait(base + UART_LSR * 4, UART_LSR_THRE, UART_LSR_THRE); ++ prom_putchar_wait(base + UART_LSR * 4, BOTH_EMPTY, BOTH_EMPTY); + __raw_writel(ch, base + UART_TX * 4); +- prom_putchar_wait(base + UART_LSR * 4, UART_LSR_THRE, UART_LSR_THRE); ++ prom_putchar_wait(base + UART_LSR * 4, BOTH_EMPTY, BOTH_EMPTY); + } + + static void prom_putchar_ar933x(unsigned char ch) diff --git a/target/linux/ar71xx/patches-3.18/521-MIPS-ath79-enable-UART-for-early_serial.patch b/target/linux/ar71xx/patches-3.18/521-MIPS-ath79-enable-UART-for-early_serial.patch index 3d6ddfe18c..e546ff26fe 100644 --- a/target/linux/ar71xx/patches-3.18/521-MIPS-ath79-enable-UART-for-early_serial.patch +++ b/target/linux/ar71xx/patches-3.18/521-MIPS-ath79-enable-UART-for-early_serial.patch @@ -1,6 +1,6 @@ --- a/arch/mips/ath79/early_printk.c +++ b/arch/mips/ath79/early_printk.c -@@ -56,6 +56,46 @@ static void prom_putchar_dummy(unsigned +@@ -58,6 +58,46 @@ static void prom_putchar_dummy(unsigned /* nothing to do */ } @@ -47,7 +47,7 @@ static void prom_putchar_init(void) { void __iomem *base; -@@ -86,8 +126,10 @@ static void prom_putchar_init(void) +@@ -88,8 +128,10 @@ static void prom_putchar_init(void) default: _prom_putchar = prom_putchar_dummy; diff --git a/target/linux/ar71xx/patches-3.18/707-MIPS-ath79-add-support-for-QCA953x-SoC.patch b/target/linux/ar71xx/patches-3.18/707-MIPS-ath79-add-support-for-QCA953x-SoC.patch index 88d376cd55..e432c6f3b6 100644 --- a/target/linux/ar71xx/patches-3.18/707-MIPS-ath79-add-support-for-QCA953x-SoC.patch +++ b/target/linux/ar71xx/patches-3.18/707-MIPS-ath79-add-support-for-QCA953x-SoC.patch @@ -22,7 +22,7 @@ meaning of the bits CPUCLK_FROM_CPUPLL and DDRCLK_FROM_DDRPLL is reversed. --- a/arch/mips/ath79/Kconfig +++ b/arch/mips/ath79/Kconfig -@@ -1257,6 +1257,10 @@ config SOC_AR934X +@@ -1266,6 +1266,10 @@ config SOC_AR934X select PCI_AR724X if PCI def_bool n @@ -33,7 +33,7 @@ meaning of the bits CPUCLK_FROM_CPUPLL and DDRCLK_FROM_DDRPLL is reversed. config SOC_QCA955X select HW_HAS_PCI select PCI_AR724X if PCI -@@ -1299,7 +1303,7 @@ config ATH79_DEV_USB +@@ -1308,7 +1312,7 @@ config ATH79_DEV_USB def_bool n config ATH79_DEV_WMAC @@ -275,7 +275,7 @@ meaning of the bits CPUCLK_FROM_CPUPLL and DDRCLK_FROM_DDRPLL is reversed. else --- a/arch/mips/ath79/early_printk.c +++ b/arch/mips/ath79/early_printk.c -@@ -114,6 +114,8 @@ static void prom_putchar_init(void) +@@ -116,6 +116,8 @@ static void prom_putchar_init(void) case REV_ID_MAJOR_AR9341: case REV_ID_MAJOR_AR9342: case REV_ID_MAJOR_AR9344: diff --git a/target/linux/ar71xx/patches-3.18/735-MIPS-ath79-add-support-for-QCA956x-SoC.patch b/target/linux/ar71xx/patches-3.18/735-MIPS-ath79-add-support-for-QCA956x-SoC.patch index 6d836adb52..b5c88e9b99 100644 --- a/target/linux/ar71xx/patches-3.18/735-MIPS-ath79-add-support-for-QCA956x-SoC.patch +++ b/target/linux/ar71xx/patches-3.18/735-MIPS-ath79-add-support-for-QCA956x-SoC.patch @@ -211,7 +211,7 @@ --- a/arch/mips/ath79/early_printk.c +++ b/arch/mips/ath79/early_printk.c -@@ -118,6 +118,8 @@ static void prom_putchar_init(void) +@@ -120,6 +120,8 @@ static void prom_putchar_init(void) case REV_ID_MAJOR_QCA9533_V2: case REV_ID_MAJOR_QCA9556: case REV_ID_MAJOR_QCA9558: @@ -378,7 +378,7 @@ } --- a/arch/mips/ath79/Kconfig +++ b/arch/mips/ath79/Kconfig -@@ -1277,6 +1277,12 @@ config SOC_QCA955X +@@ -1286,6 +1286,12 @@ config SOC_QCA955X select PCI_AR724X if PCI def_bool n @@ -391,7 +391,7 @@ config ATH79_DEV_M25P80 select ATH79_DEV_SPI def_bool n -@@ -1314,7 +1320,7 @@ config ATH79_DEV_USB +@@ -1323,7 +1329,7 @@ config ATH79_DEV_USB def_bool n config ATH79_DEV_WMAC -- 2.30.2