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kdb: Simplify code to fetch characters from console

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Currently kdb_read_get_key() contains complex control flow that, on
close inspection, turns out to be unnecessary. In particular:

1. It is impossible to enter the branch conditioned on (escape_delay == 1)
   except when the loop enters with (escape_delay == 2) allowing us to
   combine the branches.

2. Most of the code conditioned on (escape_delay == 2) simply modifies
   local data and then breaks out of the loop causing the function to
   return escape_data[0].

3. Based on #2 there is not actually any need to ever explicitly set
   escape_delay to 2 because we it is much simpler to directly return
   escape_data[0] instead.

4. escape_data[0] is, for all but one exit path, known to be '\e'.

Simplify the code based on these observations.

There is a subtle (and harmless) change of behaviour resulting from this
simplification: instead of letting the escape timeout after ~1998
milliseconds we now timeout after ~2000 milliseconds

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20191025073328.643-3-daniel.thompson@linaro.org
This commit is contained in:
Daniel Thompson 2019-10-25 08:33:25 +01:00
parent 53b63136e8
commit d04213af90
1 changed files with 14 additions and 24 deletions
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38
kernel/debug/kdb/kdb_io.c
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@ -124,25 +124,18 @@ static int kdb_read_get_key(char *buffer, size_t bufsize)
touch_nmi_watchdog();
f = &kdb_poll_funcs[0];
}
if (escape_delay == 2) {
*ped = '\0';
ped = escape_data;
--escape_delay;
}
if (escape_delay == 1) {
key = *ped++;
if (!*ped)
--escape_delay;
break;
}
key = (*f)();
if (key == -1) {
if (escape_delay) {
udelay(ESCAPE_UDELAY);
--escape_delay;
if (--escape_delay == 0)
return '\e';
}
continue;
}
if (bufsize <= 2) {
if (key == '\r')
key = '\n';
@ -150,27 +143,24 @@ static int kdb_read_get_key(char *buffer, size_t bufsize)
*buffer = '\0';
return -1;
}
if (escape_delay == 0 && key == '\e') {
escape_delay = ESCAPE_DELAY;
ped = escape_data;
f_escape = f;
}
if (escape_delay) {
*ped++ = key;
if (f_escape != f) {
escape_delay = 2;
continue;
}
if (f_escape != f)
return '\e';
*ped++ = key;
key = kdb_handle_escape(escape_data, ped - escape_data);
if (key > 0) {
escape_data[0] = key;
escape_data[1] = '\0';
}
if (key)
escape_delay = 2;
continue;
if (key < 0)
return '\e';
if (key == 0)
continue;
}
break; /* A key to process */
}
return key;