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@xxxxxxxxxxxxxx>
---
v2: rebased to latest code
drivers/tty/serial/amba-pl011.c | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index c0da0cc..69b5acd 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1167,7 +1167,7 @@ static void pl011_dma_shutdown(struct uart_amba_port *uap)
/* 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 @@ static void pl011_put_poll_char(struct uart_port *port,
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 @@ static void pl011_console_putchar(struct uart_port *port, int ch)
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 @@ static void
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 @@ pl011_console_write(struct console *co, const char *s, unsigned int count)
* 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 struct console amba_console = {
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)
--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.
--
To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
