serial/amba-pl011: Disable interrupts around TX softirq

pl011_tx_softirq() currently uses spin_{,un}lock(), which are not
sufficient to inhibit pl011_int() from being triggered by a local
IRQ and trying to re-take the same lock.  This can lead to
deadlocks.

This patch uses the _irq() locking variants instead to ensure that
pl011_int() handling for a given port is deferred until any
pl011_tx_softirq() work for that port is complete.

Notes for stable:

This patch fixes an issue that is fixed by the following upstream
commit, which is a more substantial rewrite of the affected code,
fixing multiple, mostly more minor issues:

        1e84d22322ceed4767db1e5342c830dd60c8210f
        serial/amba-pl011: Refactor and simplify TX FIFO handling

The upstream patch was rejected for stable on the reasonable grounds
that it was too big and complex a patch.  The original buggy code was
merged in v4.1, and the rewrite was merged in v4.2, leaving only v4.1
affected.

This patch replaces the 1e84d22, for 4.1.x only.

Fixes: 734745caeb9f serial/amba-pl011: Activate TX IRQ passively
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Tested-by: Robin Murphy <robin.murphy@arm.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 763eb20fe3213b6cfda04dc2624bcd1b8638f324..0cc622afb67d43baa9850cbca52a2ee687e76254 100644 (file)
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1360,9 +1360,9 @@ static void pl011_tx_softirq(struct work_struct *work)
        struct uart_amba_port *uap =
                container_of(dwork, struct uart_amba_port, tx_softirq_work);
 
-       spin_lock(&uap->port.lock);
+       spin_lock_irq(&uap->port.lock);
        while (pl011_tx_chars(uap)) ;
-       spin_unlock(&uap->port.lock);
+       spin_unlock_irq(&uap->port.lock);
 }
 
 static void pl011_tx_irq_seen(struct uart_amba_port *uap)