On Friday 04 May 2007, Corey Minyard wrote:
>I did think of one other thing: if you clear the MSR delta flags while
>polling the serial console, you need to call the routine to check the
>modem status since the interrupt will not happen. So here's the
>patch...
>
>Subject: Serial 8250: Handle saving the clear-on-read bits from the LSR and
> MSR
>
I applied this patch because I was curious to see what effect if any it had on
some serial based acessories I use here, like a cm11 x10 controller with
heyu, and a belkin ups with its supplied software.
But at first boot, its not 100% operationally safe, but please read on.
1) heyu (the x10 control program) is now stuck in a loop, repeating the last
command issued, at about 40 second repeat intervals. AND it is using 90%+ of
the cpu while it executes each loop, which takes about 7 to 10 seconds each
time. heyu is interfacing to the world via /dev/ttyUSB0, through an FTDI
adapter so I'm not able to make a mental connection here between this patch
and that effect.
2) HOWEVER! The belkin upsd daemon, which started being a cpu hog, using 40%
of the cpu continuously since something in the 2.6.20 to 2.6.21 time frame,
and this was regardless of whether it was talking through a /dev/ttyUSB# port
and either a pl2303, or an FTDI adaptor, or direct through /dev/ttyS0, is at
least for /dev/ttyS0, now operating normally and apparently 100% stable. So
I pulled out another FTDI adaptor, and reconfigured the daemon to
use /dev/ttyUSB1, and that is also operating 100% normally now.
Can someone explain 1) above? Even odder still, I'd killed and restarted heyu
several times to no avail before I tried putting upsd on /dev/ttyUSB1, but
after moving the upsd access from /dev/ttyS0 to /dev/ttyUSB1, then heyu,
running through /dev/ttyUSB0, is now operating 100% normally. ???
Does anyone have any idea what kind of bait I should put out to kill this
nilmerg? I'm happy, its all working again for a change, but I'll be damned
if I ain't totally bumfuzzled. And I wonder if it will survive a reboot...
>Reading the LSR clears the break, parity, frame error, and overrun
>bits in the 8250 chip, but these are not being saved in all places
>that read the LSR. Same goes for the MSR delta bits. Save the LSR
>bits off whenever the lsr is read so they can be handled later in the
>receive routine. Save the MSR bits to be handled in the modem status
>routine.
>
>Also, clear the stored bits and clear the interrupt registers before
>enabling interrupts, to avoid handling old values of the stored bits
>in the interrupt routines.
>
>Signed-off-by: Corey Minyard <[email protected]>
>Cc: Russell King <[email protected]>
>
> drivers/serial/8250.c | 85
> +++++++++++++++++++++++++++++---------------- include/linux/serial_reg.h |
> 1
> 2 files changed, 57 insertions(+), 29 deletions(-)
>
>Index: linux-2.6.21/drivers/serial/8250.c
>===================================================================
>--- linux-2.6.21.orig/drivers/serial/8250.c
>+++ linux-2.6.21/drivers/serial/8250.c
>@@ -129,7 +129,16 @@ struct uart_8250_port {
> unsigned char mcr;
> unsigned char mcr_mask; /* mask of user bits */
> unsigned char mcr_force; /* mask of forced bits */
>- unsigned char lsr_break_flag;
>+
>+ /*
>+ * Some bits in registers are cleared on a read, so they must
>+ * be saved whenever the register is read but the bits will not
>+ * be immediately processed.
>+ */
>+#define LSR_SAVE_FLAGS UART_LSR_BRK_ERROR_BITS
>+ unsigned char lsr_saved_flags;
>+#define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA
>+ unsigned char msr_saved_flags;
>
> /*
> * We provide a per-port pm hook.
>@@ -1159,6 +1168,7 @@ static void serial8250_start_tx(struct u
> if (up->bugs & UART_BUG_TXEN) {
> unsigned char lsr, iir;
> lsr = serial_in(up, UART_LSR);
>+ up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
> iir = serial_in(up, UART_IIR);
> if (lsr & UART_LSR_TEMT && iir & UART_IIR_NO_INT)
> transmit_chars(up);
>@@ -1208,18 +1218,10 @@ receive_chars(struct uart_8250_port *up,
> flag = TTY_NORMAL;
> up->port.icount.rx++;
>
>-#ifdef CONFIG_SERIAL_8250_CONSOLE
>- /*
>- * Recover the break flag from console xmit
>- */
>- if (up->port.line == up->port.cons->index) {
>- lsr |= up->lsr_break_flag;
>- up->lsr_break_flag = 0;
>- }
>-#endif
>+ lsr |= up->lsr_saved_flags;
>+ up->lsr_saved_flags = 0;
>
>- if (unlikely(lsr & (UART_LSR_BI | UART_LSR_PE |
>- UART_LSR_FE | UART_LSR_OE))) {
>+ if (unlikely(lsr & UART_LSR_BRK_ERROR_BITS)) {
> /*
> * For statistics only
> */
>@@ -1310,6 +1312,8 @@ static unsigned int check_modem_status(s
> {
> unsigned int status = serial_in(up, UART_MSR);
>
>+ status |= up->msr_saved_flags;
>+ up->msr_saved_flags = 0;
> if (status & UART_MSR_ANY_DELTA && up->ier & UART_IER_MSI &&
> up->port.info != NULL) {
> if (status & UART_MSR_TERI)
>@@ -1496,7 +1500,8 @@ static void serial8250_timeout(unsigned
> static void serial8250_backup_timeout(unsigned long data)
> {
> struct uart_8250_port *up = (struct uart_8250_port *)data;
>- unsigned int iir, ier = 0;
>+ unsigned int iir, ier = 0, lsr;
>+ unsigned long flags;
>
> /*
> * Must disable interrupts or else we risk racing with the interrupt
>@@ -1515,9 +1520,13 @@ static void serial8250_backup_timeout(un
> * the "Diva" UART used on the management processor on many HP
> * ia64 and parisc boxes.
> */
>+ spin_lock_irqsave(&up->port.lock, flags);
>+ lsr = serial_in(up, UART_LSR);
>+ up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
>+ spin_unlock_irqrestore(&up->port.lock, flags);
> if ((iir & UART_IIR_NO_INT) && (up->ier & UART_IER_THRI) &&
> (!uart_circ_empty(&up->port.info->xmit) || up->port.x_char) &&
>- (serial_in(up, UART_LSR) & UART_LSR_THRE)) {
>+ (lsr & UART_LSR_THRE)) {
> iir &= ~(UART_IIR_ID | UART_IIR_NO_INT);
> iir |= UART_IIR_THRI;
> }
>@@ -1536,13 +1545,14 @@ static unsigned int serial8250_tx_empty(
> {
> struct uart_8250_port *up = (struct uart_8250_port *)port;
> unsigned long flags;
>- unsigned int ret;
>+ unsigned int lsr;
>
> spin_lock_irqsave(&up->port.lock, flags);
>- ret = serial_in(up, UART_LSR) & UART_LSR_TEMT ? TIOCSER_TEMT : 0;
>+ lsr = serial_in(up, UART_LSR);
>+ up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
> spin_unlock_irqrestore(&up->port.lock, flags);
>
>- return ret;
>+ return lsr & UART_LSR_TEMT ? TIOCSER_TEMT : 0;
> }
>
> static unsigned int serial8250_get_mctrl(struct uart_port *port)
>@@ -1613,8 +1623,7 @@ static inline void wait_for_xmitr(struct
> do {
> status = serial_in(up, UART_LSR);
>
>- if (status & UART_LSR_BI)
>- up->lsr_break_flag = UART_LSR_BI;
>+ up->lsr_saved_flags |= status & LSR_SAVE_FLAGS;
>
> if (--tmout == 0)
> break;
>@@ -1623,8 +1632,12 @@ static inline void wait_for_xmitr(struct
>
> /* Wait up to 1s for flow control if necessary */
> if (up->port.flags & UPF_CONS_FLOW) {
>- tmout = 1000000;
>- while (!(serial_in(up, UART_MSR) & UART_MSR_CTS) && --tmout) {
>+ unsigned int tmout;
>+ for (tmout = 1000000; tmout; tmout--) {
>+ unsigned int msr = serial_in(up, UART_MSR);
>+ up->msr_saved_flags |= msr & MSR_SAVE_FLAGS;
>+ if (msr & UART_MSR_CTS)
>+ break;
> udelay(1);
> touch_nmi_watchdog();
> }
>@@ -1794,6 +1807,18 @@ static int serial8250_startup(struct uar
> spin_unlock_irqrestore(&up->port.lock, flags);
>
> /*
>+ * Clear the interrupt registers again for luck, and clear the
>+ * saved flags to avoid getting false values from polling
>+ * routines or the previous session.
>+ */
>+ (void) serial_inp(up, UART_LSR);
>+ (void) serial_inp(up, UART_RX);
>+ (void) serial_inp(up, UART_IIR);
>+ (void) serial_inp(up, UART_MSR);
>+ up->lsr_saved_flags = 0;
>+ up->msr_saved_flags = 0;
>+
>+ /*
> * Finally, enable interrupts. Note: Modem status interrupts
> * are set via set_termios(), which will be occurring imminently
> * anyway, so we don't enable them here.
>@@ -1811,14 +1836,6 @@ static int serial8250_startup(struct uar
> (void) inb_p(icp);
> }
>
>- /*
>- * And clear the interrupt registers again for luck.
>- */
>- (void) serial_inp(up, UART_LSR);
>- (void) serial_inp(up, UART_RX);
>- (void) serial_inp(up, UART_IIR);
>- (void) serial_inp(up, UART_MSR);
>-
> return 0;
> }
>
>@@ -2387,6 +2404,16 @@ serial8250_console_write(struct console
> wait_for_xmitr(up, BOTH_EMPTY);
> serial_out(up, UART_IER, ier);
>
>+ /*
>+ * The receive handling will happen properly because the
>+ * receive ready bit will still be set; it is not cleared
>+ * on read. However, modem control will not, we must
>+ * call it if we have saved something in the saved flags
>+ * while processing with interrupts off.
>+ */
>+ if (up->msr_saved_flags)
>+ check_modem_status(up);
>+
> if (locked)
> spin_unlock(&up->port.lock);
> local_irq_restore(flags);
>Index: linux-2.6.21/include/linux/serial_reg.h
>===================================================================
>--- linux-2.6.21.orig/include/linux/serial_reg.h
>+++ linux-2.6.21/include/linux/serial_reg.h
>@@ -116,6 +116,7 @@
> #define UART_LSR_PE 0x04 /* Parity error indicator */
> #define UART_LSR_OE 0x02 /* Overrun error indicator */
> #define UART_LSR_DR 0x01 /* Receiver data ready */
>+#define UART_LSR_BRK_ERROR_BITS 0x1E /* BI, FE, PE, OE bits */
>
> #define UART_MSR 6 /* In: Modem Status Register */
> #define UART_MSR_DCD 0x80 /* Data Carrier Detect */
>-
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--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
#define NULL 0 /* silly thing is, we don't even use this */
-- Larry Wall in perl.c from the perl source code
-
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