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Commit 2f2fd089 authored by Timur Tabi's avatar Timur Tabi Committed by Greg Kroah-Hartman
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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: default avatarTimur Tabi <timur@codeaurora.org>
Reviewed-by: default avatarDave Martin <Dave.Martin@arm.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent b7ed5161

drivers/tty/serial/amba-pl011.c

+8 −9
Original line number Diff line number Diff line
@@ -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)