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hvc_console: Do not set low_latency when using interrupts 

hvc_console is setting low_latency unconditionally, but some clients are
interrupt driven and will call hvc_poll from irq context.  This will cause
tty_flip_buffer_push to be called from irq context, and it very clearly
states it must not be called from IRQ when low_latency is specified.

Looking back through history:
v2.6.16-rc1 via 33f0f88f1c
    [PATCH] TTY layer buffering revamp

added this new api.

v2.6.16-rc3 via 8977d929e4
    [PATCH] tty buffering stall fix

claims to fix a stall discovered with hvc_console

v2.6.16-rc5 via fb5c594c2a
   [PATCH] Fix race condition in hvc console.

said set this flag to avoid a stall problem, and was merged through
the powerpc arch tree.

Without searching for email discussions, it would appear to be an
overlapping "fix", but one that did not consider all users.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Milton Miller 2009-01-08 02:14:24 +00:00 committed by Benjamin Herrenschmidt
parent c21f7a527f
commit da9dc13289
1 changed files with 2 additions and 1 deletions
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3
drivers/char/hvc_console.c
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@ -318,7 +318,8 @@ static int hvc_open(struct tty_struct *tty, struct file * filp)
} /* else count == 0 */
tty->driver_data = hp;
tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */
if (!hp->irq_requested)
tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */
hp->tty = tty;