serial: amba-pl011: use cpu_relax when polling registers
Busy loops that poll on a register should call cpu_relax(). On some
architectures, it can lower CPU power consumption or yield to a
hyperthreaded twin processor. It also serves as a compiler barrier,
so it can replace barrier() calls.
Signed-off-by: Timur Tabi <timur@codeaurora.org>
Reviewed-by: Dave Martin <Dave.Martin@arm.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 de84602..618763b 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1167,7 +1167,7 @@
/* Disable RX and TX DMA */
while (pl011_read(uap, REG_FR) & UART01x_FR_BUSY)
- barrier();
+ cpu_relax();
spin_lock_irq(&uap->port.lock);
uap->dmacr &= ~(UART011_DMAONERR | UART011_RXDMAE | UART011_TXDMAE);
@@ -1611,7 +1611,7 @@
container_of(port, struct uart_amba_port, port);
while (pl011_read(uap, REG_FR) & UART01x_FR_TXFF)
- barrier();
+ cpu_relax();
pl011_write(ch, uap, REG_DR);
}
@@ -2150,7 +2150,7 @@
container_of(port, struct uart_amba_port, port);
while (pl011_read(uap, REG_FR) & UART01x_FR_TXFF)
- barrier();
+ cpu_relax();
pl011_write(ch, uap, REG_DR);
}
@@ -2158,7 +2158,7 @@
pl011_console_write(struct console *co, const char *s, unsigned int count)
{
struct uart_amba_port *uap = amba_ports[co->index];
- unsigned int status, old_cr = 0, new_cr;
+ unsigned int old_cr = 0, new_cr;
unsigned long flags;
int locked = 1;
@@ -2188,9 +2188,8 @@
* Finally, wait for transmitter to become empty
* and restore the TCR
*/
- do {
- status = pl011_read(uap, REG_FR);
- } while (status & UART01x_FR_BUSY);
+ while (pl011_read(uap, REG_FR) & UART01x_FR_BUSY)
+ cpu_relax();
if (!uap->vendor->always_enabled)
pl011_write(old_cr, uap, REG_CR);
@@ -2302,13 +2301,13 @@
static void pl011_putc(struct uart_port *port, int c)
{
while (readl(port->membase + UART01x_FR) & UART01x_FR_TXFF)
- ;
+ cpu_relax();
if (port->iotype == UPIO_MEM32)
writel(c, port->membase + UART01x_DR);
else
writeb(c, port->membase + UART01x_DR);
while (readl(port->membase + UART01x_FR) & UART01x_FR_BUSY)
- ;
+ cpu_relax();
}
static void pl011_early_write(struct console *con, const char *s, unsigned n)