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Re: [PATCH] serial driver PMC MSP71xx, kernel linux-mips.git master

To: Marc St-Jean <Marc_St-Jean@pmc-sierra.com>
Subject: Re: [PATCH] serial driver PMC MSP71xx, kernel linux-mips.git master
From: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Date: Thu, 25 Jan 2007 17:50:34 +0300
Cc: linux-mips@linux-mips.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
In-reply-to: <45B7F32E.1030208@pmc-sierra.com>
Organization: MontaVista Software Inc.
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <45B7F32E.1030208@pmc-sierra.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mozilla/5.0 (X11; U; Linux i686; rv:1.7.2) Gecko/20040803
Marc St-Jean wrote:
Here is my second attempt at the serial driver patch for the
PMC-Sierra MSP71xx device.

There are three different fixes:
1. Fix for THRE errata
- I verified the UART_BUG_TXEN fix does not help with this erratum.
- I left our current fix in until I get our platform booting on
2.6.20-rc4 to try the mm tree "8250-uart-backup-timer.patch".
Feel free to ignore for now.

2. Fix for Busy Detect on LCR write
- Moved to new UPIO_DWAPB iotype. Because the new type is a memory
mapped device and there are several tests for UPIO_MEM, this involved
updating serial_core.c and 8250_early.c in addition to 8250.c.
- I tried implementing this totally in serial_in as suggested, but
it can't be done because of bit overlap between UART_IIR_NO_INT and
UART_IIR_BUSY. Also there is no way to set the interrupt "handled = 1"
from serial_in.

3. Workaround for interrupt/data concurrency issue
- Moved to new UPIO_DWAPB iotype.

Index: linux_2_6/drivers/serial/8250.c
===================================================================
RCS file: linux_2_6/drivers/serial/8250.c,v
retrieving revision 1.1.1.7
diff -u -r1.1.1.7 8250.c
--- linux_2_6/drivers/serial/8250.c     19 Oct 2006 21:00:58 -0000      1.1.1.7
+++ linux_2_6/drivers/serial/8250.c     24 Jan 2007 23:55:27 -0000
[...]
@@ -333,6 +334,8 @@
  static void
  serial_out(struct uart_8250_port *up, int offset, int value)

Your patch is clearly garbled again, something added an extra space to all lines stating with space... :-/

  {
+       /* Save the offset before it's remapped */
+       int save_offset = offset;

   Is there real need to save this? What regshift equals for this UART?

        offset = map_8250_out_reg(up, offset) << up->port.regshift;

        switch (up->port.iotype) {
@@ -359,6 +362,19 @@
                        writeb(value, up->port.membase + offset);
                break;

+       case UPIO_DWAPB:
+               /* Save the LCR value so it can be re-written when a
+                * Busy Detect interrupt occurs. */
+               if (save_offset == UART_LCR)
+                       up->lcr = value;
+               writeb(value, up->port.membase + offset);
+               /* Read the IER to ensure any interrupt is cleared before
+                * returning from ISR. */
+               if ((save_offset == UART_TX || save_offset == UART_IER) &&

   Not sure how an IER read ensures that...

+                               in_irq())

I'd suggest to either indent this line right (start below 2ns paren of if stmt) or keep on the same line.

+                       value = serial_in(up, UART_IER);
+               break;
+               
        default:
                outb(value, up->port.iobase + offset);
        }
@@ -1016,6 +1032,17 @@
                up->bugs |= UART_BUG_NOMSR;
  #endif

+       /* Workaround:
+        * The DesignWare SoC UART part has a bug for all
+        * versions before 3.03a (2005-07-18)
+        * In brief, this is a non-standard 16550 in that the THRE interrupt
+        * will not re-assert itself simply by disabling and re-enabling the
+        * THRI bit in the IER, it is only re-enabled if a character is actually
+        * sent out.
+        */
+       if( up->port.flags & UPF_DW_THRE_BUG )
+               up->bugs |= UART_BUG_DWTHRE;
+
        serial_outp(up, UART_LCR, save_lcr);

        if (up->capabilities != uart_config[up->port.type].flags) {
@@ -1141,6 +1168,12 @@
                        iir = serial_in(up, UART_IIR);
                        if (lsr & UART_LSR_TEMT && iir & UART_IIR_NO_INT)
                                transmit_chars(up);
+               } else if (up->bugs & UART_BUG_DWTHRE) {
+                       unsigned char lsr, iir;
+                       lsr = serial_in(up, UART_LSR);
+                       iir = serial_in(up, UART_IIR);
+                       if (lsr & UART_LSR_THRE)

   Why read IIR if you don't check it?

@@ -2352,9 +2402,12 @@

        add_preferred_console("ttyS", line, options);
        printk("Adding console on ttyS%d at %s 0x%lx (options '%s')\n",
-               line, port->iotype == UPIO_MEM ? "MMIO" : "I/O port",
-               port->iotype == UPIO_MEM ? (unsigned long) port->mapbase :
-                   (unsigned long) port->iobase, options);
+               line,
+               (port->iotype == UPIO_MEM || port->iotype == UPIO_DWAPB)
+                       ? "MMIO" : "I/O port",
+               (port->iotype == UPIO_MEM || port->iotype == UPIO_DWAPB)
+                       ? (unsigned long) port->mapbase : (unsigned long) 
port->iobase,
+               options);
        if (!(serial8250_console.flags & CON_ENABLED)) {
                serial8250_console.flags &= ~CON_PRINTBUFFER;
                register_console(&serial8250_console);
[...]
Index: linux_2_6/drivers/serial/8250_early.c
===================================================================
RCS file: linux_2_6/drivers/serial/8250_early.c,v
retrieving revision 1.1.1.3
diff -u -r1.1.1.3 8250_early.c
--- linux_2_6/drivers/serial/8250_early.c       19 Oct 2006 20:08:20 -0000      
1.1.1.3
+++ linux_2_6/drivers/serial/8250_early.c       24 Jan 2007 23:55:27 -0000
@@ -46,7 +46,7 @@

  static unsigned int __init serial_in(struct uart_port *port, int offset)
  {
-       if (port->iotype == UPIO_MEM)
+       if (port->iotype == UPIO_MEM || port->iotype == UPIO_DWAPB)
                return readb(port->membase + offset);
        else
                return inb(port->iobase + offset);
@@ -54,7 +54,7 @@

  static void __init serial_out(struct uart_port *port, int offset, int value)
  {
-       if (port->iotype == UPIO_MEM)
+       if (port->iotype == UPIO_MEM || port->iotype == UPIO_DWAPB)
                writeb(value, port->membase + offset);
        else
                outb(value, port->iobase + offset);
@@ -233,7 +233,7 @@
                return 0;

        /* Try to start the normal driver on a matching line.  */
-       mmio = (port->iotype == UPIO_MEM);
+       mmio = (port->iotype == UPIO_MEM || port->iotype == UPIO_DWAPB);
        line = serial8250_start_console(port, device->options);
        if (line < 0)
                printk("No ttyS device at %s 0x%lx for console\n",

From your 8250_eraly.c changes I can conclude regshift == 1 (it doesn't currently support other cases). So, serial_pot() doesn't need save_offset. :-)

Index: linux_2_6/drivers/serial/serial_core.c
===================================================================
RCS file: linux_2_6/drivers/serial/serial_core.c,v
retrieving revision 1.1.1.7
diff -u -r1.1.1.7 serial_core.c
--- linux_2_6/drivers/serial/serial_core.c      19 Oct 2006 21:00:58 -0000      
1.1.1.7
+++ linux_2_6/drivers/serial/serial_core.c      24 Jan 2007 23:55:28 -0000
@@ -1669,9 +1669,10 @@

        ret = sprintf(buf, "%d: uart:%s %s%08lX irq:%d",
                        port->line, uart_type(port),
-                       port->iotype == UPIO_MEM ? "mmio:0x" : "port:",
-                       port->iotype == UPIO_MEM ? port->mapbase :
-                                               (unsigned long) port->iobase,
+                       (port->iotype == UPIO_MEM || port->iotype == UPIO_DWAPB)
+                               ? "mmio:0x" : "port:",
+                       (port->iotype == UPIO_MEM || port->iotype == UPIO_DWAPB)
+                               ? port->mapbase : (unsigned long) port->iobase,
                        port->irq);
        if (port->type == PORT_UNKNOWN) {

Needless change. My patch that fixes this function is in Linus' tree since September, not sure why you don't have it:

http://www2.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=6c6a2334a1e8af7c3eaab992732825fa9ade77cf

Index: linux_2_6/include/linux/serial_core.h
===================================================================
RCS file: linux_2_6/include/linux/serial_core.h,v
retrieving revision 1.1.1.7
diff -u -r1.1.1.7 serial_core.h
--- linux_2_6/include/linux/serial_core.h       19 Oct 2006 21:01:02 -0000      
1.1.1.7
+++ linux_2_6/include/linux/serial_core.h       24 Jan 2007 23:55:28 -0000
[...]
@@ -274,6 +277,7 @@
        struct device           *dev;                   /* parent device */
        unsigned char           hub6;                   /* this should be in 
the 8250 driver */
        unsigned char           unused[3];
+       void                            *user;                  /* generic 
platform 'user' pointer */

Erm, 'private' or 'data' would've sounded better in the kernel context, IMHO... :-)

Index: linux_2_6/include/linux/serial_reg.h
===================================================================
RCS file: linux_2_6/include/linux/serial_reg.h,v
retrieving revision 1.1.1.2
diff -u -r1.1.1.2 serial_reg.h
--- linux_2_6/include/linux/serial_reg.h        19 Oct 2006 18:29:50 -0000      
1.1.1.2
+++ linux_2_6/include/linux/serial_reg.h        24 Jan 2007 23:55:29 -0000
@@ -218,6 +218,10 @@
  #define UART_FCR_PXAR16       0x80    /* receive FIFO treshold = 16 */
  #define UART_FCR_PXAR32       0xc0    /* receive FIFO treshold = 32 */

+/*
+ * DesignWare APB UART
+ */
+#define UART_IIR_BUSY          0x07    /* Busy Detect */

I'd suggest keeping this with other UART_IIR_* #defines, separated by the more elaborate comment.

WBR, Sergei

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