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ar71xx: fix nondeterministic hangs during bootconsole/console handover

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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
This commit is contained in:
John Crispin 2016-04-09 10:26:37 +00:00
parent 240ed52317
commit 2cba297ea0
2 changed files with 108 additions and 0 deletions
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54
target/linux/ar71xx/patches-4.1/003-MIPS-ath79-make-bootconsole-wait-for-both-THRE-and-T.patch Normal file
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@ -0,0 +1,54 @@
From f1ba020af5076172c9d29006a747ccf40027fedc Mon Sep 17 00:00:00 2001
Message-Id: <f1ba020af5076172c9d29006a747ccf40027fedc.1458840219.git.mschiffer@universe-factory.net>
From: Matthias Schiffer <mschiffer@universe-factory.net>
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: <stable@vger.kernel.org>
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
---
arch/mips/ath79/early_printk.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/mips/ath79/early_printk.c b/arch/mips/ath79/early_printk.c
index b955faf..d1adc59 100644
--- a/arch/mips/ath79/early_printk.c
+++ b/arch/mips/ath79/early_printk.c
@@ -31,13 +31,15 @@ static inline void prom_putchar_wait(void __iomem *reg, u32 mask, u32 val)
} 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)
--
2.7.4

54
target/linux/ar71xx/patches-4.4/003-MIPS-ath79-make-bootconsole-wait-for-both-THRE-and-T.patch Normal file
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@ -0,0 +1,54 @@
From f1ba020af5076172c9d29006a747ccf40027fedc Mon Sep 17 00:00:00 2001
Message-Id: <f1ba020af5076172c9d29006a747ccf40027fedc.1458840219.git.mschiffer@universe-factory.net>
From: Matthias Schiffer <mschiffer@universe-factory.net>
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: <stable@vger.kernel.org>
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
---
arch/mips/ath79/early_printk.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/mips/ath79/early_printk.c b/arch/mips/ath79/early_printk.c
index b955faf..d1adc59 100644
--- a/arch/mips/ath79/early_printk.c
+++ b/arch/mips/ath79/early_printk.c
@@ -31,13 +31,15 @@ static inline void prom_putchar_wait(void __iomem *reg, u32 mask, u32 val)
} 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)
--
2.7.4