On Wed, May 06, 2020 at 07:23:31AM -0400, Mikulas Patocka wrote:
> The patch 92d7223a74235054f2aa7227d207d9c57f84dca0 ("alpha: io: reorder
> barriers to guarantee writeX() and iowriteX() ordering #2") broke boot on
> the Alpha Avanti platform.
>
> The patch changes timing between accesses to the ISA bus, in particular,
> it reduces the time between "write" access and a subsequent "read" access.
>
> This causes lock-up when accessing the real time clock and serial ports.
>
> This patch fixes the serial ports by adding a small delay before the "inb"
> instruction.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2")
> Cc: stable@xxxxxxxxxxxxxxx # v4.17+
>
> ---
> drivers/tty/serial/8250/8250_port.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> Index: linux-stable/drivers/tty/serial/8250/8250_port.c
> ===================================================================
> --- linux-stable.orig/drivers/tty/serial/8250/8250_port.c 2020-05-06 08:25:19.000000000 +0200
> +++ linux-stable/drivers/tty/serial/8250/8250_port.c 2020-05-06 09:04:17.000000000 +0200
> @@ -442,6 +442,10 @@ static unsigned int mem32be_serial_in(st
>
> static unsigned int io_serial_in(struct uart_port *p, int offset)
> {
> +#ifdef CONFIG_ALPHA
> +/* we need a small delay, the Alpha Avanti chipset locks up with back-to-back accesses */
> + ndelay(300);
> +#endif
We really do not like #ifdef in .c files, especially ones that cause a
coding style violation :)
Why can't you do this as a quirk for this specific chipset? You should
tie it to the serial port hardware type, not to the CPU type.
thanks,
greg k-h
