Linux 4.14.111

[thirdparty/kernel/stable-queue.git] / releases / 4.14.111 / tty-increase-the-default-flip-buffer-limit-to-2-640k.patch

diff --git a/releases/4.14.111/tty-increase-the-default-flip-buffer-limit-to-2-640k.patch b/releases/4.14.111/tty-increase-the-default-flip-buffer-limit-to-2-640k.patch
new file mode 100644 (file)
index 0000000..2ca68fd
--- /dev/null
+++ b/releases/4.14.111/tty-increase-the-default-flip-buffer-limit-to-2-640k.patch
@@ -0,0 +1,51 @@
+From ec2c61630594a2b7c0abde742e06113737db017c Mon Sep 17 00:00:00 2001
+From: Manfred Schlaegl <manfred.schlaegl@ginzinger.com>
+Date: Mon, 28 Jan 2019 19:01:10 +0100
+Subject: tty: increase the default flip buffer limit to 2*640K
+
+[ Upstream commit 7ab57b76ebf632bf2231ccabe26bea33868118c6 ]
+
+We increase the default limit for buffer memory allocation by a factor of
+10 to 640K to prevent data loss when using fast serial interfaces.
+
+For example when using RS485 without flow-control at speeds of 1Mbit/s
+an upwards we've run into problems such as applications being too slow
+to read out this buffer (on embedded devices based on imx53 or imx6).
+
+If you want to write transmitted data to a slow SD card and thus have
+realtime requirements, this limit can become a problem.
+
+That shouldn't be the case and 640K buffers fix such problems for us.
+
+This value is a maximum limit for allocation only. It has no effect
+on systems that currently run fine. When transmission is slow enough
+applications and hardware can keep up and increasing this limit
+doesn't change anything.
+
+It only _allows_ to allocate more than 2*64K in cases we currently fail to
+allocate memory despite having some.
+
+Signed-off-by: Manfred Schlaegl <manfred.schlaegl@ginzinger.com>
+Signed-off-by: Martin Kepplinger <martin.kepplinger@ginzinger.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+Signed-off-by: Sasha Levin <sashal@kernel.org>
+---
+ drivers/tty/tty_buffer.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
+index 217114227f8d..cf11882d2602 100644
+--- a/drivers/tty/tty_buffer.c
++++ b/drivers/tty/tty_buffer.c
+@@ -25,7 +25,7 @@
+  * Byte threshold to limit memory consumption for flip buffers.
+  * The actual memory limit is > 2x this amount.
+  */
+-#define TTYB_DEFAULT_MEM_LIMIT        65536
++#define TTYB_DEFAULT_MEM_LIMIT        (640 * 1024UL)
+ 
+ /*
+  * We default to dicing tty buffer allocations to this many characters
+-- 
+2.19.1
+