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>
---
drivers/tty/serial/amba-pl011.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 005de8c..164bd65 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1076,7 +1076,7 @@ static void pl011_dma_shutdown(struct uart_amba_port *uap)
/* Disable RX and TX DMA */
while (readw(uap->port.membase + UART01x_FR) & UART01x_FR_BUSY)
- barrier();
+ cpu_relax();
spin_lock_irq(&uap->port.lock);
uap->dmacr &= ~(UART011_DMAONERR | UART011_RXDMAE | UART011_TXDMAE);
@@ -1520,7 +1520,7 @@ static void pl011_put_poll_char(struct uart_port *port,
container_of(port, struct uart_amba_port, port);
while (readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF)
- barrier();
+ cpu_relax();
writew(ch, uap->port.membase + UART01x_DR);
}
@@ -2053,7 +2053,7 @@ static void pl011_console_putchar(struct uart_port *port, int ch)
container_of(port, struct uart_amba_port, port);
while (readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF)
- barrier();
+ cpu_relax();
writew(ch, uap->port.membase + UART01x_DR);
}
@@ -2093,6 +2093,7 @@ pl011_console_write(struct console *co, const char *s, unsigned int count)
*/
do {
status = readw(uap->port.membase + UART01x_FR);
+ cpu_relax();
} while (status & UART01x_FR_BUSY);
if (!uap->vendor->always_enabled)
writew(old_cr, uap->port.membase + UART011_CR);
@@ -2205,10 +2206,10 @@ static struct console amba_console = {
static void pl011_putc(struct uart_port *port, int c)
{
while (readl(port->membase + UART01x_FR) & UART01x_FR_TXFF)
- barrier();
+ cpu_relax();
writel(c, port->membase + UART01x_DR);
while (!(readl(port->membase + UART01x_FR) & UART011_FR_TXFE))
- barrier();
+ 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.
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