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91861a69 SL |
1 | From 23e06916e49c59645d67c4c710aeb2bcaefbe675 Mon Sep 17 00:00:00 2001 |
2 | From: Manfred Schlaegl <manfred.schlaegl@ginzinger.com> | |
3 | Date: Mon, 28 Jan 2019 19:01:10 +0100 | |
4 | Subject: tty: increase the default flip buffer limit to 2*640K | |
5 | ||
6 | [ Upstream commit 7ab57b76ebf632bf2231ccabe26bea33868118c6 ] | |
7 | ||
8 | We increase the default limit for buffer memory allocation by a factor of | |
9 | 10 to 640K to prevent data loss when using fast serial interfaces. | |
10 | ||
11 | For example when using RS485 without flow-control at speeds of 1Mbit/s | |
12 | an upwards we've run into problems such as applications being too slow | |
13 | to read out this buffer (on embedded devices based on imx53 or imx6). | |
14 | ||
15 | If you want to write transmitted data to a slow SD card and thus have | |
16 | realtime requirements, this limit can become a problem. | |
17 | ||
18 | That shouldn't be the case and 640K buffers fix such problems for us. | |
19 | ||
20 | This value is a maximum limit for allocation only. It has no effect | |
21 | on systems that currently run fine. When transmission is slow enough | |
22 | applications and hardware can keep up and increasing this limit | |
23 | doesn't change anything. | |
24 | ||
25 | It only _allows_ to allocate more than 2*64K in cases we currently fail to | |
26 | allocate memory despite having some. | |
27 | ||
28 | Signed-off-by: Manfred Schlaegl <manfred.schlaegl@ginzinger.com> | |
29 | Signed-off-by: Martin Kepplinger <martin.kepplinger@ginzinger.com> | |
30 | Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> | |
31 | Signed-off-by: Sasha Levin <sashal@kernel.org> | |
32 | --- | |
33 | drivers/tty/tty_buffer.c | 2 +- | |
34 | 1 file changed, 1 insertion(+), 1 deletion(-) | |
35 | ||
36 | diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c | |
37 | index 355e9cad680d..4706df20191b 100644 | |
38 | --- a/drivers/tty/tty_buffer.c | |
39 | +++ b/drivers/tty/tty_buffer.c | |
40 | @@ -25,7 +25,7 @@ | |
41 | * Byte threshold to limit memory consumption for flip buffers. | |
42 | * The actual memory limit is > 2x this amount. | |
43 | */ | |
44 | -#define TTYB_DEFAULT_MEM_LIMIT 65536 | |
45 | +#define TTYB_DEFAULT_MEM_LIMIT (640 * 1024UL) | |
46 | ||
47 | /* | |
48 | * We default to dicing tty buffer allocations to this many characters | |
49 | -- | |
50 | 2.19.1 | |
51 |