[PATCH] ar71xx-make-bootconsole-wait-for-both-THRE-and-TEMT

[Christian Dresel]

Fix the Race Condition on boot



Signed-off-by: Christian Dresel <fff at chrisi01.de>

	new file:   build_patches/openwrt/0005-ar71xx-make-bootconsole-wait-for-both-THRE-and-TEMT.patch
---
 ...e-bootconsole-wait-for-both-THRE-and-TEMT.patch | 86 ++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 build_patches/openwrt/0005-ar71xx-make-bootconsole-wait-for-both-THRE-and-TEMT.patch

diff --git a/build_patches/openwrt/0005-ar71xx-make-bootconsole-wait-for-both-THRE-and-TEMT.patch b/build_patches/openwrt/0005-ar71xx-make-bootconsole-wait-for-both-THRE-and-TEMT.patch
new file mode 100644
index 0000000..ada44bc
--- /dev/null
+++ b/build_patches/openwrt/0005-ar71xx-make-bootconsole-wait-for-both-THRE-and-TEMT.patch
@@ -0,0 +1,86 @@
+From: Matthias Schiffer <mschiffer at universe-factory.net>
+Date: Thu, 24 Mar 2016 18:30:26 +0100
+Subject: ar71xx: make bootconsole wait for both THRE and TEMT
+
+Original commit message:
+
+    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.)
+
+diff --git a/target/linux/ar71xx/patches-3.18/103-MIPS-ath79-make-bootconsole-wait-for-both-THRE-and-T.patch b/target/linux/ar71xx/patches-3.18/103-MIPS-ath79-make-bootconsole-wait-for-both-THRE-and-T.patch
+new file mode 100644
+index 0000000..7be14ab
+--- /dev/null
++++ b/target/linux/ar71xx/patches-3.18/103-MIPS-ath79-make-bootconsole-wait-for-both-THRE-and-T.patch
+@@ -0,0 +1,54 @@
++From f1ba020af5076172c9d29006a747ccf40027fedc Mon Sep 17 00:00:00 2001
++Message-Id: <f1ba020af5076172c9d29006a747ccf40027fedc.1458840219.git.mschiffer at universe-factory.net>
++From: Matthias Schiffer <mschiffer at 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 at vger.kernel.org>
++Signed-off-by: Matthias Schiffer <mschiffer at 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
++
+
-- 
2.1.4