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serial: amba-pl011: use cpu_relax when polling registers

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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>
This commit is contained in:
Timur Tabi 2016-01-15 14:32:20 -06:00 committed by Greg Kroah-Hartman
parent b7ed5161f1
commit 2f2fd08949
1 changed files with 8 additions and 9 deletions
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17
drivers/tty/serial/amba-pl011.c
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@ -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)