[SUNSAB]: Defer register updates until transmitter is idle.

The chip can emit garbage characters if we touch the
settings while characters are going out.

Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 72 insertions, 38 deletions

diff --git a/drivers/serial/sunsab.c b/drivers/serial/sunsab.c
index 39b788d95e39..10e2990a40d4 100644
--- a/drivers/serial/sunsab.c
+++ b/drivers/serial/sunsab.c
@@ -61,6 +61,16 @@ struct uart_sunsab_port {
         unsigned char                   pvr_dtr_bit;    /* Which PVR bit is DTR */
         unsigned char                   pvr_dsr_bit;    /* Which PVR bit is DSR */
         int                             type;           /* SAB82532 version     */
+
+        /* Setting configuration bits while the transmitter is active
+         * can cause garbage characters to get emitted by the chip.
+         * Therefore, we cache such writes here and do the real register
+         * write the next time the transmitter becomes idle.
+         */
+        unsigned int                    cached_ebrg;
+        unsigned char                   cached_mode;
+        unsigned char                   cached_pvr;
+        unsigned char                   cached_dafo;
 };
 
 /*
@@ -236,6 +246,7 @@ receive_chars(struct uart_sunsab_port *up,
 }
 
 static void sunsab_stop_tx(struct uart_port *, unsigned int);
+static void sunsab_tx_idle(struct uart_sunsab_port *);
 
 static void transmit_chars(struct uart_sunsab_port *up,
                            union sab82532_irq_status *stat)
@@ -258,6 +269,7 @@ static void transmit_chars(struct uart_sunsab_port *up,
                 return;
 
         set_bit(SAB82532_XPR, &up->irqflags);
+        sunsab_tx_idle(up);
 
         if (uart_circ_empty(xmit) || uart_tx_stopped(&up->port)) {
                 up->interrupt_mask1 |= SAB82532_IMR1_XPR;
@@ -397,21 +409,21 @@ static void sunsab_set_mctrl(struct uart_port *port, unsigned int mctrl)
         struct uart_sunsab_port *up = (struct uart_sunsab_port *) port;
 
         if (mctrl & TIOCM_RTS) {
-                writeb(readb(&up->regs->rw.mode) & ~SAB82532_MODE_FRTS,
-                       &up->regs->rw.mode);
-                writeb(readb(&up->regs->rw.mode) | SAB82532_MODE_RTS,
-                       &up->regs->rw.mode);
+                up->cached_mode &= ~SAB82532_MODE_FRTS;
+                up->cached_mode |= SAB82532_MODE_RTS;
         } else {
-                writeb(readb(&up->regs->rw.mode) | SAB82532_MODE_FRTS,
-                       &up->regs->rw.mode);
-                writeb(readb(&up->regs->rw.mode) | SAB82532_MODE_RTS,
-                       &up->regs->rw.mode);
+                up->cached_mode |= (SAB82532_MODE_FRTS |
+                                    SAB82532_MODE_RTS);
         }
         if (mctrl & TIOCM_DTR) {
-                writeb(readb(&up->regs->rw.pvr) & ~(up->pvr_dtr_bit), &up->regs->rw.pvr);
+                up->cached_pvr &= ~(up->pvr_dtr_bit);
         } else {
-                writeb(readb(&up->regs->rw.pvr) | up->pvr_dtr_bit, &up->regs->rw.pvr);
+                up->cached_pvr |= up->pvr_dtr_bit;
         }
+
+        set_bit(SAB82532_REGS_PENDING, &up->irqflags);
+        if (test_bit(SAB82532_XPR, &up->irqflags))
+                sunsab_tx_idle(up);
 }
 
 /* port->lock is not held.  */
@@ -450,6 +462,25 @@ static void sunsab_stop_tx(struct uart_port *port, unsigned int tty_stop)
 }
 
 /* port->lock held by caller.  */
+static void sunsab_tx_idle(struct uart_sunsab_port *up)
+{
+        if (test_bit(SAB82532_REGS_PENDING, &up->irqflags)) {
+                u8 tmp;
+
+                clear_bit(SAB82532_REGS_PENDING, &up->irqflags);
+                writeb(up->cached_mode, &up->regs->rw.mode);
+                writeb(up->cached_pvr, &up->regs->rw.pvr);
+                writeb(up->cached_dafo, &up->regs->w.dafo);
+
+                writeb(up->cached_ebrg & 0xff, &up->regs->w.bgr);
+                tmp = readb(&up->regs->rw.ccr2);
+                tmp &= ~0xc0;
+                tmp |= (up->cached_ebrg >> 2) & 0xc0;
+                writeb(tmp, &up->regs->rw.ccr2);
+        }
+}
+
+/* port->lock held by caller.  */
 static void sunsab_start_tx(struct uart_port *port, unsigned int tty_start)
 {
         struct uart_sunsab_port *up = (struct uart_sunsab_port *) port;
@@ -517,12 +548,16 @@ static void sunsab_break_ctl(struct uart_port *port, int break_state)
 
         spin_lock_irqsave(&up->port.lock, flags);
 
-        val = readb(&up->regs->rw.dafo);
+        val = up->cached_dafo;
         if (break_state)
                 val |= SAB82532_DAFO_XBRK;
         else
                 val &= ~SAB82532_DAFO_XBRK;
-        writeb(val, &up->regs->rw.dafo);
+        up->cached_dafo = val;
+
+        set_bit(SAB82532_REGS_PENDING, &up->irqflags);
+        if (test_bit(SAB82532_XPR, &up->irqflags))
+                sunsab_tx_idle(up);
 
         spin_unlock_irqrestore(&up->port.lock, flags);
 }
@@ -566,8 +601,9 @@ static int sunsab_startup(struct uart_port *port)
                SAB82532_CCR2_TOE, &up->regs->w.ccr2);
         writeb(0, &up->regs->w.ccr3);
         writeb(SAB82532_CCR4_MCK4 | SAB82532_CCR4_EBRG, &up->regs->w.ccr4);
-        writeb(SAB82532_MODE_RTS | SAB82532_MODE_FCTS |
-               SAB82532_MODE_RAC, &up->regs->w.mode);
+        up->cached_mode = (SAB82532_MODE_RTS | SAB82532_MODE_FCTS |
+                           SAB82532_MODE_RAC);
+        writeb(up->cached_mode, &up->regs->w.mode);
         writeb(SAB82532_RFC_DPS|SAB82532_RFC_RFTH_32, &up->regs->w.rfc);
         
         tmp = readb(&up->regs->rw.ccr0);
@@ -598,7 +634,6 @@ static void sunsab_shutdown(struct uart_port *port)
 {
         struct uart_sunsab_port *up = (struct uart_sunsab_port *) port;
         unsigned long flags;
-        unsigned char tmp;
 
         spin_lock_irqsave(&up->port.lock, flags);
 
@@ -609,14 +644,13 @@ static void sunsab_shutdown(struct uart_port *port)
         writeb(up->interrupt_mask1, &up->regs->w.imr1);
 
         /* Disable break condition */
-        tmp = readb(&up->regs->rw.dafo);
-        tmp &= ~SAB82532_DAFO_XBRK;
-        writeb(tmp, &up->regs->rw.dafo);
+        up->cached_dafo = readb(&up->regs->rw.dafo);
+        up->cached_dafo &= ~SAB82532_DAFO_XBRK;
+        writeb(up->cached_dafo, &up->regs->rw.dafo);
 
         /* Disable Receiver */  
-        tmp = readb(&up->regs->rw.mode);
-        tmp &= ~SAB82532_MODE_RAC;
-        writeb(tmp, &up->regs->rw.mode);
+        up->cached_mode &= ~SAB82532_MODE_RAC;
+        writeb(up->cached_mode, &up->regs->rw.mode);
 
         /*
          * XXX FIXME
@@ -685,7 +719,6 @@ static void sunsab_convert_to_sab(struct uart_sunsab_port *up, unsigned int cfla
                                   unsigned int iflag, unsigned int baud,
                                   unsigned int quot)
 {
-        unsigned int ebrg;
         unsigned char dafo;
         int bits, n, m;
 
@@ -714,10 +747,11 @@ static void sunsab_convert_to_sab(struct uart_sunsab_port *up, unsigned int cfla
         } else {
                 dafo |= SAB82532_DAFO_PAR_EVEN;
         }
+        up->cached_dafo = dafo;
 
         calc_ebrg(baud, &n, &m);
 
-        ebrg = n | (m << 6);
+        up->cached_ebrg = n | (m << 6);
 
         up->tec_timeout = (10 * 1000000) / baud;
         up->cec_timeout = up->tec_timeout >> 2;
@@ -770,16 +804,13 @@ static void sunsab_convert_to_sab(struct uart_sunsab_port *up, unsigned int cfla
         uart_update_timeout(&up->port, cflag,
                             (up->port.uartclk / (16 * quot)));
 
-        /* Now bang the new settings into the chip.  */
-        sunsab_cec_wait(up);
-        sunsab_tec_wait(up);
-        writeb(dafo, &up->regs->w.dafo);
-        writeb(ebrg & 0xff, &up->regs->w.bgr);
-        writeb((readb(&up->regs->rw.ccr2) & ~0xc0) | ((ebrg >> 2) & 0xc0),
-               &up->regs->rw.ccr2);
-
-        writeb(readb(&up->regs->rw.mode) | SAB82532_MODE_RAC, &up->regs->rw.mode);
-
+        /* Now schedule a register update when the chip's
+         * transmitter is idle.
+         */
+        up->cached_mode |= SAB82532_MODE_RAC;
+        set_bit(SAB82532_REGS_PENDING, &up->irqflags);
+        if (test_bit(SAB82532_XPR, &up->irqflags))
+                sunsab_tx_idle(up);
 }
 
 /* port->lock is not held.  */
@@ -1084,11 +1115,13 @@ static void __init sunsab_init_hw(void)
                         up->pvr_dsr_bit = (1 << 3);
                         up->pvr_dtr_bit = (1 << 2);
                 }
-                writeb((1 << 1) | (1 << 2) | (1 << 4), &up->regs->w.pvr);
-                writeb(readb(&up->regs->rw.mode) | SAB82532_MODE_FRTS,
-                       &up->regs->rw.mode);
-                writeb(readb(&up->regs->rw.mode) | SAB82532_MODE_RTS,
-                       &up->regs->rw.mode);
+                up->cached_pvr = (1 << 1) | (1 << 2) | (1 << 4);
+                writeb(up->cached_pvr, &up->regs->w.pvr);
+                up->cached_mode = readb(&up->regs->rw.mode);
+                up->cached_mode |= SAB82532_MODE_FRTS;
+                writeb(up->cached_mode, &up->regs->rw.mode);
+                up->cached_mode |= SAB82532_MODE_RTS;
+                writeb(up->cached_mode, &up->regs->rw.mode);
 
                 up->tec_timeout = SAB82532_MAX_TEC_TIMEOUT;
                 up->cec_timeout = SAB82532_MAX_CEC_TIMEOUT;
diff --git a/drivers/serial/sunsab.h b/drivers/serial/sunsab.h
index 686086fcbbf5..b78e1f7b8050 100644
--- a/drivers/serial/sunsab.h
+++ b/drivers/serial/sunsab.h
@@ -126,6 +126,7 @@ union sab82532_irq_status {
 /* irqflags bits */
 #define SAB82532_ALLS                   0x00000001
 #define SAB82532_XPR                    0x00000002
+#define SAB82532_REGS_PENDING           0x00000004
 
 /* RFIFO Status Byte */
 #define SAB82532_RSTAT_PE               0x80