Commit b6adea33 authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab Committed by Linus Torvalds
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8250: fix boot hang with serial console when using with Serial Over Lan port 



Intel 8257x Ethernet boards have a feature called Serial Over Lan.

This feature works by emulating a serial port, and it is detected by
kernel as a normal 8250 port.  However, this emulation is not perfect, as
also noticed on changeset 7500b1f6.

Before this patch, the kernel were trying to check if the serial TX is
capable of work using IRQ's.

This were done with a code similar this:

        serial_outp(up, UART_IER, UART_IER_THRI);
        lsr = serial_in(up, UART_LSR);
        iir = serial_in(up, UART_IIR);
        serial_outp(up, UART_IER, 0);

        if (lsr & UART_LSR_TEMT && iir & UART_IIR_NO_INT)
		up->bugs |= UART_BUG_TXEN;

This works fine for other 8250 ports, but, on 8250-emulated SoL port, the
chip is a little lazy to down UART_IIR_NO_INT at UART_IIR register.

Due to that, UART_BUG_TXEN is sometimes enabled.  However, as TX IRQ keeps
working, and the TX polling is now enabled, the driver miss-interprets the
IRQ received later, hanging up the machine until a key is pressed at the
serial console.

This is the 6 version of this patch.  Previous versions were trying to
introduce a large enough delay between serial_outp and serial_in(up,
UART_IIR), but not taking forever.  However, the needed delay couldn't be
safely determined.

At the experimental tests, a delay of 1us solves most of the cases, but
still hangs sometimes.  Increasing the delay to 5us was better, but still
doesn't solve.  A very high delay of 50 ms seemed to work every time.

However, poking around with delays and pray for it to be enough doesn't
seem to be a good approach, even for a quirk.

So, instead of playing with random large arbitrary delays, let's just
disable UART_BUG_TXEN for all SoL ports.

[akpm@linux-foundation.org: fix warnings]
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@redhat.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: <stable@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3cf31140

drivers/serial/8250.c

+15 −0
Original line number Diff line number Diff line
@@ -2083,6 +2083,20 @@ static int serial8250_startup(struct uart_port *port) 


	serial8250_set_mctrl(&up->port, up->port.mctrl);



	/* Serial over Lan (SoL) hack:

	   Intel 8257x Gigabit ethernet chips have a

	   16550 emulation, to be used for Serial Over Lan.

	   Those chips take a longer time than a normal

	   serial device to signalize that a transmission

	   data was queued. Due to that, the above test generally

	   fails. One solution would be to delay the reading of

	   iir. However, this is not reliable, since the timeout

	   is variable. So, let's just don't test if we receive

	   TX irq. This way, we'll never enable UART_BUG_TXEN.

	 */

	if (up->port.flags & UPF_NO_TXEN_TEST)

		goto dont_test_tx_en;



	/*

	 * Do a quick test to see if we receive an

	 * interrupt when we enable the TX irq.
@@ -2102,6 +2116,7 @@ static int serial8250_startup(struct uart_port *port) 
		up->bugs &= ~UART_BUG_TXEN;

	}



dont_test_tx_en:

	spin_unlock_irqrestore(&up->port.lock, flags);



	/*

drivers/serial/8250_pci.c

+36 −0
Original line number Diff line number Diff line
@@ -798,6 +798,21 @@ pci_default_setup(struct serial_private *priv, 
	return setup_port(priv, port, bar, offset, board->reg_shift);

}



static int skip_tx_en_setup(struct serial_private *priv,

			const struct pciserial_board *board,

			struct uart_port *port, int idx)

{

	port->flags |= UPF_NO_TXEN_TEST;

	printk(KERN_DEBUG "serial8250: skipping TxEn test for device "

			  "[%04x:%04x] subsystem [%04x:%04x]\n",

			  priv->dev->vendor,

			  priv->dev->device,

			  priv->dev->subsystem_vendor,

			  priv->dev->subsystem_device);



	return pci_default_setup(priv, board, port, idx);

}



/* This should be in linux/pci_ids.h */

#define PCI_VENDOR_ID_SBSMODULARIO	0x124B

#define PCI_SUBVENDOR_ID_SBSMODULARIO	0x124B
@@ -864,6 +879,27 @@ static struct pci_serial_quirk pci_serial_quirks[] __refdata = { 
		.init		= pci_inteli960ni_init,

		.setup		= pci_default_setup,

	},

	{

		.vendor		= PCI_VENDOR_ID_INTEL,

		.device		= PCI_DEVICE_ID_INTEL_8257X_SOL,

		.subvendor	= PCI_ANY_ID,

		.subdevice	= PCI_ANY_ID,

		.setup		= skip_tx_en_setup,

	},

	{

		.vendor		= PCI_VENDOR_ID_INTEL,

		.device		= PCI_DEVICE_ID_INTEL_82573L_SOL,

		.subvendor	= PCI_ANY_ID,

		.subdevice	= PCI_ANY_ID,

		.setup		= skip_tx_en_setup,

	},

	{

		.vendor		= PCI_VENDOR_ID_INTEL,

		.device		= PCI_DEVICE_ID_INTEL_82573E_SOL,

		.subvendor	= PCI_ANY_ID,

		.subdevice	= PCI_ANY_ID,

		.setup		= skip_tx_en_setup,

	},

	/*

	 * ITE

	 */

include/linux/pci_ids.h

+3 −0
Original line number Diff line number Diff line
@@ -2323,6 +2323,9 @@ 
#define PCI_DEVICE_ID_INTEL_82378	0x0484

#define PCI_DEVICE_ID_INTEL_I960	0x0960

#define PCI_DEVICE_ID_INTEL_I960RM	0x0962

#define PCI_DEVICE_ID_INTEL_8257X_SOL	0x1062

#define PCI_DEVICE_ID_INTEL_82573E_SOL	0x1085

#define PCI_DEVICE_ID_INTEL_82573L_SOL	0x108F

#define PCI_DEVICE_ID_INTEL_82815_MC	0x1130

#define PCI_DEVICE_ID_INTEL_82815_CGC	0x1132

#define PCI_DEVICE_ID_INTEL_82092AA_0	0x1221

include/linux/serial_core.h

+1 −0
Original line number Diff line number Diff line
@@ -296,6 +296,7 @@ struct uart_port { 
#define UPF_HARDPPS_CD		((__force upf_t) (1 << 11))

#define UPF_LOW_LATENCY		((__force upf_t) (1 << 13))

#define UPF_BUGGY_UART		((__force upf_t) (1 << 14))

#define UPF_NO_TXEN_TEST	((__force upf_t) (1 << 15))

#define UPF_MAGIC_MULTIPLIER	((__force upf_t) (1 << 16))

#define UPF_CONS_FLOW		((__force upf_t) (1 << 23))

#define UPF_SHARE_IRQ		((__force upf_t) (1 << 24))

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