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Subject[PATCH v4 2/3] serial/8250_pci: Clear FIFOs for Intel ME Serial Over Lan device on BI
From
Date
From: Sudhakar Mamillapalli <sudhakar@fb.com>

When using Serial Over Lan (SOL) over the virtual serial port in a Intel
management engine (ME) device, on device reset the serial FIFOs need to
be cleared to keep the FIFO indexes in-sync between the host and the
engine.

On a reset the serial device assertes BI, so using that as a cue FIFOs
are cleared. So for this purpose a new handle_break callback has been
added. One other problem is that the serial registers might temporarily
go to 0 on reset of this device. So instead of using the IER register
read, if 0 returned use the ier value in uart_8250_port. This is hidden
under a custom serial_in.

Cc: Nhan H Mai <nhan.h.mai@intel.com>
Signed-off-by: Sudhakar Mamillapalli <sudhakar@fb.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/tty/serial/8250/8250.c | 10 +++++++++
drivers/tty/serial/8250/8250.h | 2 ++
drivers/tty/serial/8250/8250_pci.c | 39 ++++++++++++++++++++++++++++++++++++
3 files changed, 51 insertions(+)
diff --git a/drivers/tty/serial/8250/8250.c b/drivers/tty/serial/8250/8250.c
index cbd94c3..182efcc 100644
--- a/drivers/tty/serial/8250/8250.c
+++ b/drivers/tty/serial/8250/8250.c
@@ -568,6 +568,16 @@ static void serial8250_clear_fifos(struct uart_8250_port *p)
}
}

+void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
+{
+ unsigned char fcr;
+
+ serial8250_clear_fifos(p);
+ fcr = uart_config[p->port.type].fcr;
+ serial_out(p, UART_FCR, fcr);
+}
+EXPORT_SYMBOL_GPL(serial8250_clear_and_reinit_fifos);
+
/*
* IER sleep support. UARTs which have EFRs need the "extended
* capability" bit enabled. Note that on XR16C850s, we need to
diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 2868a1d..c9d0ebe 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -96,6 +96,8 @@ static inline void serial_out(struct uart_8250_port *up, int offset, int value)
up->port.serial_out(&up->port, offset, value);
}

+void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p);
+
#if defined(__alpha__) && !defined(CONFIG_PCI)
/*
* Digital did something really horribly wrong with the OUT1 and OUT2
diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
index 858dca8..024551a 100644
--- a/drivers/tty/serial/8250/8250_pci.c
+++ b/drivers/tty/serial/8250/8250_pci.c
@@ -17,6 +17,7 @@
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/tty.h>
+#include <linux/serial_reg.h>
#include <linux/serial_core.h>
#include <linux/8250_pci.h>
#include <linux/bitops.h>
@@ -1092,11 +1093,49 @@ static int skip_tx_en_setup(struct serial_private *priv,
return pci_default_setup(priv, board, port, idx);
}

+static void kt_handle_break(struct uart_port *p)
+{
+ struct uart_8250_port *up =
+ container_of(p, struct uart_8250_port, port);
+ /*
+ * On receipt of a BI, serial device in Intel ME (Intel
+ * management engine) needs to have its fifos cleared for sane
+ * SOL (Serial Over Lan) output.
+ */
+ serial8250_clear_and_reinit_fifos(up);
+}
+
+static unsigned int kt_serial_in(struct uart_port *p, int offset)
+{
+ struct uart_8250_port *up =
+ container_of(p, struct uart_8250_port, port);
+ unsigned int val;
+
+ /*
+ * When the Intel ME (management engine) gets reset its serial
+ * port registers could return 0 momentarily. Functions like
+ * serial8250_console_write, read and save the IER, perform
+ * some operation and then restore it. In order to avoid
+ * setting IER register inadvertently to 0, if the value read
+ * is 0, double check with ier value in uart_8250_port and use
+ * that instead. up->ier should be the same value as what is
+ * currently configured.
+ */
+ val = inb(p->iobase + offset);
+ if (offset == UART_IER) {
+ if (val == 0)
+ val = up->ier;
+ }
+ return val;
+}
+
static int kt_serial_setup(struct serial_private *priv,
const struct pciserial_board *board,
struct uart_port *port, int idx)
{
port->flags |= UPF_BUG_THRE;
+ port->serial_in = kt_serial_in;
+ port->handle_break = kt_handle_break;
return skip_tx_en_setup(priv, board, port, idx);
}



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