On 08/11/2015 08:40 AM, Russell King - ARM Linux wrote:
> On Mon, Aug 10, 2015 at 08:31:03PM -0400, Peter Hurley wrote:
>> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
>> index 2af09ab..fd54991 100644
>> --- a/drivers/tty/serial/amba-pl011.c
>> +++ b/drivers/tty/serial/amba-pl011.c
>> @@ -2348,13 +2348,10 @@ static struct console amba_console = {
>>
>> static void pl011_putc(struct uart_port *port, int c)
>> {
>> - struct uart_amba_port *uap =
>> - container_of(port, struct uart_amba_port, port);
>> -
>> - while (pl011_readw(uap, REG_FR) & UART01x_FR_TXFF)
>> + while (readl(port->membase + UART01x_FR) & UART01x_FR_TXFF)
>> ;
>> - pl011_writeb(uap, c, REG_DR);
>> - while (pl011_readw(uap, REG_FR) & uap->fr_busy)
>> + writeb(c, port->membase + UART01x_DR);
>> + while (readl(port->membase + UART01x_FR) & UART01x_FR_BUSY)
>> ;
>
> These loops are wrong. Kernel coding style is that loops like this
> will use cpu_relax() in them, just like the driver used to. This
> was introduced by:
>
> commit 0d3c673e7881e691991b2a4745bd4f149603baa2
> Author: Rob Herring <robh@xxxxxxxxxx>
> Date: Fri Apr 18 17:19:57 2014 -0500
>
> tty/serial: pl011: add generic earlycon support
>
> Also, the above readl()s should be readl_relaxed(), we don't need
> barriered reads or to hit the L2 cache on those reads in the above code.
This patch just reverts pl011 earlycon back to the existing mainline
state.
The amba-pl011 driver has many places where cpu_relax() is not used,
so that seems like a good patch for -next during the 4.3-rc cycle.
Similarly for read_relaxed() use in earlycon.
Regards,
Peter Hurley
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