From dfcf8a8dbe2e77b7b5797838d809e778dba0ff9f Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= Date: Wed, 20 Apr 2016 06:05:56 +0000 Subject: 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 git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@49202 3c298f89-4303-0410-b956-a3cf2f4a3e73 --- ...make-bootconsole-wait-for-both-THRE-and-T.patch | 49 ++++++++++++++++++++++ 1 file changed, 49 insertions(+) create mode 100644 target/linux/ar71xx/patches-3.18/003-MIPS-ath79-make-bootconsole-wait-for-both-THRE-and-T.patch (limited to '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) -- cgit v1.2.3