linux/ar71xx: add an ath79_serial upstream patch

diff --git a/target/linux/ar71xx/patches-4.1/999_ath79_serial_fix.patch b/target/linux/ar71xx/patches-4.1/999_ath79_serial_fix.patch
new file mode 100644 (file)
index 0000000..d805234
--- /dev/null
+++ b/target/linux/ar71xx/patches-4.1/999_ath79_serial_fix.patch
@@ -0,0 +1,47 @@
+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@xxxxxxxxxxxxxxx>
+Signed-off-by: Matthias Schiffer <mschiffer@xxxxxxxxxxxxxxxxxxxx>
+---
+ 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