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