On Wed, 6 May 2020, Greg Kroah-Hartman wrote:
> On Wed, May 06, 2020 at 01:04:38PM -0400, Mikulas Patocka wrote:
> >
> > I've created this patch that adds a global macro/variable
> > serial_port_needs_delay. I've also deleted UPQ_DELAY_BEFORE_READ and test
> > serial_port_needs_delay directly in io_serial_in, so that the compiler
> > will optimize it out on non-alpha architectures.
>
> That's not good, what about systems with hundreds of serial ports?
I doubt that someone will conect hundreds of serial ports to such an old
alpha machine :)
> > > But, there is no other way to detect this based on hardware
> > > signatures/types instead? That is usually the best way to do it, right?
> >
> > It's hard to detect Alpha without using '#ifdef CONFIG_ALPHA' :) The ISA
> > serial port hardware is simple, so I think that you can't distinguish it
> > just based on its behavior.
>
> The ISA serial port hardware does not have a unique vendor/product id
> somewhere? Some other sort of definition that we can use to determine
> exactly what type of system we are running on?
AFAIK it doesn't. You can only distinguish 8250, 16550 and 16550A - but
not the vendor.
> > Index: linux-stable/drivers/tty/serial/8250/8250_port.c
> > ===================================================================
> > --- linux-stable.orig/drivers/tty/serial/8250/8250_port.c 2020-05-06 18:54:24.000000000 +0200
> > +++ linux-stable/drivers/tty/serial/8250/8250_port.c 2020-05-06 18:54:24.000000000 +0200
> > @@ -30,6 +30,7 @@
> > #include <linux/uaccess.h>
> > #include <linux/pm_runtime.h>
> > #include <linux/ktime.h>
> > +#include <linux/pci.h>
> >
> > #include <asm/io.h>
> > #include <asm/irq.h>
> > @@ -442,6 +443,9 @@ static unsigned int mem32be_serial_in(st
> >
> > static unsigned int io_serial_in(struct uart_port *p, int offset)
> > {
> > + if (serial_port_needs_delay)
> > + ndelay(300);
>
> Again, this should be a per-port thing, not all ports in the system are
> this broken, right?
>
> thanks,
>
> greg k-h
Here is the patch that uses per-port flag UPQ_DELAY_BEFORE_READ. The flag
is activated if we have the specific PCI-ISA bridge and if the serial port
is an ISA port.
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 | 3 +++
arch/alpha/kernel/pci.c | 4 ++++
drivers/tty/serial/8250/8250_core.c | 15 +++++++++------
drivers/tty/serial/8250/8250_port.c | 3 +++
include/linux/pci.h | 4 ++++
include/linux/serial_core.h | 1 +
6 files changed, 24 insertions(+), 6 deletions(-)
Index: linux-stable/arch/alpha/include/asm/pci.h
===================================================================
--- linux-stable.orig/arch/alpha/include/asm/pci.h 2020-05-07 09:54:55.000000000 +0200
+++ linux-stable/arch/alpha/include/asm/pci.h 2020-05-07 09:54:55.000000000 +0200
@@ -97,4 +97,7 @@ 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 serial_port_needs_delay;
+#define serial_port_needs_delay serial_port_needs_delay
+
#endif /* __ALPHA_PCI_H */
Index: linux-stable/arch/alpha/kernel/pci.c
===================================================================
--- linux-stable.orig/arch/alpha/kernel/pci.c 2020-05-07 09:54:55.000000000 +0200
+++ linux-stable/arch/alpha/kernel/pci.c 2020-05-07 09:54:55.000000000 +0200
@@ -61,9 +61,13 @@ struct pci_controller *pci_isa_hose;
* Quirks.
*/
+int serial_port_needs_delay = 0;
+EXPORT_SYMBOL(serial_port_needs_delay);
+
static void quirk_isa_bridge(struct pci_dev *dev)
{
dev->class = PCI_CLASS_BRIDGE_ISA << 8;
+ 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 2020-05-07 09:54:55.000000000 +0200
+++ linux-stable/drivers/tty/serial/8250/8250_port.c 2020-05-07 09:54:55.000000000 +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);
}
Index: linux-stable/include/linux/pci.h
===================================================================
--- linux-stable.orig/include/linux/pci.h 2020-05-07 09:54:55.000000000 +0200
+++ linux-stable/include/linux/pci.h 2020-05-07 09:54:55.000000000 +0200
@@ -2384,6 +2384,10 @@ static inline bool pci_is_thunderbolt_at
return false;
}
+#ifndef serial_port_needs_delay
+#define serial_port_needs_delay 0
+#endif
+
#if defined(CONFIG_PCIEPORTBUS) || defined(CONFIG_EEH)
void pci_uevent_ers(struct pci_dev *pdev, enum pci_ers_result err_type);
#endif
Index: linux-stable/drivers/tty/serial/8250/8250_core.c
===================================================================
--- linux-stable.orig/drivers/tty/serial/8250/8250_core.c 2020-05-07 09:54:55.000000000 +0200
+++ linux-stable/drivers/tty/serial/8250/8250_core.c 2020-05-07 09:54:55.000000000 +0200
@@ -34,6 +34,7 @@
#include <linux/uaccess.h>
#include <linux/pm_runtime.h>
#include <linux/io.h>
+#include <linux/pci.h>
#ifdef CONFIG_SPARC
#include <linux/sunserialcore.h>
#endif
@@ -487,9 +488,17 @@ static void univ8250_rsa_support(struct
#define univ8250_rsa_support(x) do { } while (0)
#endif /* CONFIG_SERIAL_8250_RSA */
+/*
+ * This "device" covers _all_ ISA 8250-compatible serial devices listed
+ * in the table in include/asm/serial.h
+ */
+static struct platform_device *serial8250_isa_devs;
+
static inline void serial8250_apply_quirks(struct uart_8250_port *up)
{
up->port.quirks |= skip_txen_test ? UPQ_NO_TXEN_TEST : 0;
+ if (serial_port_needs_delay && serial8250_isa_devs && up->port.dev == &serial8250_isa_devs->dev)
+ up->port.quirks |= UPQ_DELAY_BEFORE_READ;
}
static void __init serial8250_isa_init_ports(void)
@@ -903,12 +912,6 @@ static struct platform_driver serial8250
};
/*
- * This "device" covers _all_ ISA 8250-compatible serial devices listed
- * in the table in include/asm/serial.h
- */
-static struct platform_device *serial8250_isa_devs;
-
-/*
* serial8250_register_8250_port and serial8250_unregister_port allows for
* 16x50 serial ports to be configured at run-time, to support PCMCIA
* modems and PCI multiport cards.
Index: linux-stable/include/linux/serial_core.h
===================================================================
--- linux-stable.orig/include/linux/serial_core.h 2020-05-07 09:54:55.000000000 +0200
+++ linux-stable/include/linux/serial_core.h 2020-05-07 09:54:55.000000000 +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 */
