On Wed, May 06, 2020 at 11:29:29AM -0400, Mikulas Patocka wrote:
>
>
> On Wed, 6 May 2020, Greg Kroah-Hartman wrote:
>
> > > 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
>
> Do you want this patch? It enables the delay based on the specific PCI-ISA
> bridge.
>
> There is still "#if defined(CONFIG_ALPHA) && defined(CONFIG_PCI)" because
> if we want to reference a variable defined by the PCI subsystem in the
> arch/alpha tree, we must do it conditionally. If you want to get rid of
> these #ifs, please describe how.
>
> Mikulas
>
>
> From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>
> 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+
>
> ---
> arch/alpha/include/asm/pci.h | 2 ++
> arch/alpha/kernel/pci.c | 4 ++++
> drivers/tty/serial/8250/8250_core.c | 7 +++++++
> drivers/tty/serial/8250/8250_port.c | 3 +++
> include/linux/serial_core.h | 1 +
> 5 files changed, 17 insertions(+)
>
> Index: linux-stable/include/linux/serial_core.h
> ===================================================================
> --- linux-stable.orig/include/linux/serial_core.h 2020-05-06 17:16:28.000000000 +0200
> +++ linux-stable/include/linux/serial_core.h 2020-05-06 17:16:28.000000000 +0200
> @@ -154,6 +154,7 @@ struct uart_port {
>
> /* quirks must be updated while holding port mutex */
> #define UPQ_NO_TXEN_TEST BIT(0)
> +#define UPQ_DELAY_BEFORE_READ BIT(1)
>
> unsigned int read_status_mask; /* driver specific */
> unsigned int ignore_status_mask; /* driver specific */
> Index: linux-stable/drivers/tty/serial/8250/8250_core.c
> ===================================================================
> --- linux-stable.orig/drivers/tty/serial/8250/8250_core.c 2020-05-06 17:16:28.000000000 +0200
> +++ linux-stable/drivers/tty/serial/8250/8250_core.c 2020-05-06 17:16:28.000000000 +0200
> @@ -37,6 +37,9 @@
> #ifdef CONFIG_SPARC
> #include <linux/sunserialcore.h>
> #endif
> +#if defined(CONFIG_ALPHA) && defined(CONFIG_PCI)
> +#include <linux/pci.h>
> +#endif
Don't need the #if for this.
>
> #include <asm/irq.h>
>
> @@ -490,6 +493,10 @@ static void univ8250_rsa_support(struct
> static inline void serial8250_apply_quirks(struct uart_8250_port *up)
> {
> up->port.quirks |= skip_txen_test ? UPQ_NO_TXEN_TEST : 0;
> +#if defined(CONFIG_ALPHA) && defined(CONFIG_PCI)
> + if (alpha_serial_port_needs_delay)
> + up->port.quirks |= UPQ_DELAY_BEFORE_READ;
> +#endif
Why is a #define needed here?
You can do this same type of change without any #ifdefs in any .c files
and that would be much nicer.
thanks,
greg k-h
