diff options
| author | Timur Tabi <timur@codeaurora.org> | 2016-01-15 14:32:20 -0600 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-02-06 22:51:04 -0800 |
| commit | 2f2fd0894991a04bf3581104d5ea3a8dc9a4f01f (patch) | |
| tree | 3155722dc4b757a1cb13a34ef1e6c1d31261d2c8 /drivers/tty/serial/amba-pl011.c | |
| parent | b7ed5161f17a39ed09fd799a919b5f6de688251d (diff) | |
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>
Diffstat (limited to 'drivers/tty/serial/amba-pl011.c')
| -rw-r--r-- | drivers/tty/serial/amba-pl011.c | 17 |
1 files changed, 8 insertions, 9 deletions
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index de846027ba47..618763b2539a 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) |