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
#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
}
static void __init serial8250_isa_init_ports(void)
Index: linux-stable/arch/alpha/include/asm/pci.h
===================================================================
--- linux-stable.orig/arch/alpha/include/asm/pci.h 2020-05-06 17:16:28.000000000 +0200
+++ linux-stable/arch/alpha/include/asm/pci.h 2020-05-06 17:16:28.000000000 +0200
@@ -97,4 +97,6 @@ extern void pci_adjust_legacy_attr(struc
extern int pci_create_resource_files(struct pci_dev *dev);
extern void pci_remove_resource_files(struct pci_dev *dev);
+extern int alpha_serial_port_needs_delay;
+
#endif /* __ALPHA_PCI_H */
Index: linux-stable/arch/alpha/kernel/pci.c
===================================================================
--- linux-stable.orig/arch/alpha/kernel/pci.c 2020-05-06 17:16:28.000000000 +0200
+++ linux-stable/arch/alpha/kernel/pci.c 2020-05-06 17:16:28.000000000 +0200
@@ -61,9 +61,13 @@ struct pci_controller *pci_isa_hose;
* Quirks.
*/
+int alpha_serial_port_needs_delay = 0;
+EXPORT_SYMBOL(alpha_serial_port_needs_delay);
+
static void quirk_isa_bridge(struct pci_dev *dev)
{
dev->class = PCI_CLASS_BRIDGE_ISA << 8;
+ alpha_serial_port_needs_delay = 1;
}
DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_82378, quirk_isa_bridge);
Index: linux-stable/drivers/tty/serial/8250/8250_port.c
===================================================================
--- linux-stable.orig/drivers/tty/serial/8250/8250_port.c 2020-05-06 17:16:28.000000000 +0200
+++ linux-stable/drivers/tty/serial/8250/8250_port.c 2020-05-06 17:16:32.000000000 +0200
@@ -442,6 +442,9 @@ static unsigned int mem32be_serial_in(st
static unsigned int io_serial_in(struct uart_port *p, int offset)
{
+ if (unlikely(p->quirks & UPQ_DELAY_BEFORE_READ))
+ ndelay(300);
+
offset = offset << p->regshift;
return inb(p->iobase + offset);
}
