| Message ID | alpine.LRH.2.02.2005060721450.25338@file01.intranet.prod.int.rdu2.redhat.com |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | [1/2] alpha: add a delay between RTC port write and read | expand |
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@redhat.com> > Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2") > Cc: stable@vger.kernel.org # 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
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 offset = offset << p->regshift; return inb(p->iobase + offset); }
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@redhat.com> Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2") Cc: stable@vger.kernel.org # v4.17+ --- drivers/tty/serial/8250/8250_port.c | 4 ++++ 1 file changed, 4 insertions(+)