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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 <mschiffer@universe-factory.net> SVN-Revision: 49156
55 lines
2.2 KiB
Diff
55 lines
2.2 KiB
Diff
From f1ba020af5076172c9d29006a747ccf40027fedc Mon Sep 17 00:00:00 2001
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Message-Id: <f1ba020af5076172c9d29006a747ccf40027fedc.1458840219.git.mschiffer@universe-factory.net>
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From: Matthias Schiffer <mschiffer@universe-factory.net>
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Date: Thu, 24 Mar 2016 15:34:05 +0100
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Subject: [PATCH] MIPS: ath79: make bootconsole wait for both THRE and TEMT
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This makes the ath79 bootconsole behave the same way as the generic 8250
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bootconsole.
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Also waiting for TEMT (transmit buffer is empty) instead of just THRE
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(transmit buffer is not full) ensures that all characters have been
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transmitted before the real serial driver starts reconfiguring the serial
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controller (which would sometimes result in garbage being transmitted.)
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This change does not cause a visible performance loss.
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In addition, this seems to fix a hang observed in certain configurations on
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many AR7xxx/AR9xxx SoCs during autoconfig of the real serial driver.
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A more complete follow-up patch will disable 8250 autoconfig for ath79
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altogether (the serial controller is detected as a 16550A, which is not
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fully compatible with the ath79 serial, and the autoconfig may lead to
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undefined behavior on ath79.)
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Cc: <stable@vger.kernel.org>
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Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
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---
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arch/mips/ath79/early_printk.c | 6 ++++--
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1 file changed, 4 insertions(+), 2 deletions(-)
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diff --git a/arch/mips/ath79/early_printk.c b/arch/mips/ath79/early_printk.c
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index b955faf..d1adc59 100644
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--- a/arch/mips/ath79/early_printk.c
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+++ b/arch/mips/ath79/early_printk.c
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@@ -31,13 +31,15 @@ static inline void prom_putchar_wait(void __iomem *reg, u32 mask, u32 val)
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} while (1);
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}
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+#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
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+
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static void prom_putchar_ar71xx(unsigned char ch)
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{
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void __iomem *base = (void __iomem *)(KSEG1ADDR(AR71XX_UART_BASE));
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- prom_putchar_wait(base + UART_LSR * 4, UART_LSR_THRE, UART_LSR_THRE);
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+ prom_putchar_wait(base + UART_LSR * 4, BOTH_EMPTY, BOTH_EMPTY);
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__raw_writel(ch, base + UART_TX * 4);
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- prom_putchar_wait(base + UART_LSR * 4, UART_LSR_THRE, UART_LSR_THRE);
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+ prom_putchar_wait(base + UART_LSR * 4, BOTH_EMPTY, BOTH_EMPTY);
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}
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static void prom_putchar_ar933x(unsigned char ch)
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--
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2.7.4
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