diff options
Diffstat (limited to 'target/linux/bcm27xx/patches-4.19/950-0806-tty-amba-pl011-Avoid-rare-write-when-full-error.patch')
| -rw-r--r-- | target/linux/bcm27xx/patches-4.19/950-0806-tty-amba-pl011-Avoid-rare-write-when-full-error.patch | 42 |
1 files changed, 0 insertions, 42 deletions
diff --git a/target/linux/bcm27xx/patches-4.19/950-0806-tty-amba-pl011-Avoid-rare-write-when-full-error.patch b/target/linux/bcm27xx/patches-4.19/950-0806-tty-amba-pl011-Avoid-rare-write-when-full-error.patch deleted file mode 100644 index 8deb882a98..0000000000 --- a/target/linux/bcm27xx/patches-4.19/950-0806-tty-amba-pl011-Avoid-rare-write-when-full-error.patch +++ /dev/null @@ -1,42 +0,0 @@ -From 8ef5143f743a4e922fdf0029f81452d3d7003daf Mon Sep 17 00:00:00 2001 -From: Phil Elwell <phil@raspberrypi.org> -Date: Wed, 29 Jan 2020 09:35:19 +0000 -Subject: [PATCH] tty: amba-pl011: Avoid rare write-when-full error - -Under some circumstances on BCM283x processors data loss can be -observed - a single byte missing from the TX output stream. These bytes -are always the last byte of a batch of 8 written from pl011_tx_chars -when from_irq is true, meaning that the FIFO full flag is not checked -before writing. - -The transmit optimisation relies on the FIFO being half-empty when the -TX interrupt is raised. Instrumenting the driver further showed that -the failure case correlated with the TX FIFO full flag being set at the -point where the last byte was written to the data register, which -explains the data loss but not how the FIFO appeared to be prematurely -full. A possible explanation is that a FIFO write was in flight at the -time the interrupt was raised, but as yet there is no hypothesis as to -how this might occur. - -In the absence of a clear understanding of the failure mechanism, avoid -the problem by checking the FIFO levels before writing the last byte of -the group, which will have minimal performance impact. - -Signed-off-by: Phil Elwell <phil@raspberrypi.org> ---- - drivers/tty/serial/amba-pl011.c | 4 ++++ - 1 file changed, 4 insertions(+) - ---- a/drivers/tty/serial/amba-pl011.c -+++ b/drivers/tty/serial/amba-pl011.c -@@ -1444,6 +1444,10 @@ static bool pl011_tx_chars(struct uart_a - if (likely(from_irq) && count-- == 0) - break; - -+ if (likely(from_irq) && count == 0 && -+ pl011_read(uap, REG_FR) & UART01x_FR_TXFF) -+ break; -+ - if (!pl011_tx_char(uap, xmit->buf[xmit->tail], from_irq)) - break; - |