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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: Fri, 19 Jan 2007 18:05:25 +0300
Cc: linux-mips@linux-mips.org, linux-serial@vger.kernel.org
In-reply-to: <45B00F65.6000406@pmc-sierra.com>
Organization: MontaVista Software Inc.
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <45B00F65.6000406@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
Hello.

Marc St-Jean wrote:
Here is a serial driver patch for the PMC-Sierra MSP71xx device.

There are three different fixes:
1. Fix for THRE errata
2. Fix for Busy Detect on LCR write
3. Workaround for interrupt/data concurrency issue

The first fix is handled cleanly using a UART_BUG_* flag.

   Hm, I wouldn't call it clean...

The second and third fixes use platform tests. I couldn't think of a
good way to implement them without using tests and not increase code
and structure sizes for platforms not requiring them.

Does anyone have any suggestions on implementing these without the
platform flag?

Thanks,
Marc

Signed-off-by: Marc St-Jean <Marc_St-Jean@pmc-sierra.com>

Index: linux_2_6/drivers/serial/8250.c
===================================================================
RCS file: linux_2_6/drivers/serial/8250.c,v
retrieving revision 1.1.1.7
retrieving revision 1.9
diff -u -r1.1.1.7 -r1.9
--- 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     19 Oct 2006 22:08:15 -0000      1.9
@@ -44,6 +44,10 @@
  #include <asm/io.h>
  #include <asm/irq.h>

+#ifdef CONFIG_PMC_MSP
+#include <msp_regs.h>
+#endif
+
  #include "8250.h"

  /*
@@ -130,6 +134,9 @@
        unsigned char           mcr_mask;       /* mask of user bits */
        unsigned char           mcr_force;      /* mask of forced bits */
        unsigned char           lsr_break_flag;
+#ifdef CONFIG_PMC_MSP
+       int                                     dwapb_lcr;      /* saved LCR 
for DW APB WAR */
+#endif

   There was already 'lcr' field there, couldn't it be used?

@@ -333,6 +340,10 @@
  static void
  serial_out(struct uart_8250_port *up, int offset, int value)
  {
+#ifdef CONFIG_PMC_MSP
+       /* Save the offset before it's remapped */
+       int dwapb_offset = offset;
+#endif
        offset = map_8250_out_reg(up, offset) << up->port.regshift;

        switch (up->port.iotype) {
@@ -342,7 +353,19 @@
                break;

        case UPIO_MEM:
+#ifdef CONFIG_PMC_MSP
+               /* Save the LCR value so it can be re-written when a
+                * Busy Detect interrupt occurs. */
+               if (dwapb_offset == UART_LCR)
+                       up->dwapb_lcr = value;
+#endif
                writeb(value, up->port.membase + offset);
+#ifdef CONFIG_PMC_MSP
+               /* Re-read the IER to ensure any interrupt disabling has
+                * completed before proceeding with ISR. */
+               if (dwapb_offset == UART_IER)
+                       value = serial_in(up, dwapb_offset);
+#endif
                break;

   Hm, was there really a need for #ifdef mess here?
   I'd vote for introducing new UPIO_* here, like was done for TSi10x UARTs
just for the same reason.

@@ -1016,6 +1039,17 @@
                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 +1175,12 @@
                        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)
+                               transmit_chars(up);

   I don't see how this *really* differs from the UART_BUG_TXEN case.
   Have you tried *that* workaround? In any case, looks like this errata
is auto-detectable just like UART_BUG_TXEN.

@@ -1366,6 +1406,31 @@
                        handled = 1;

                        end = NULL;
+#ifdef CONFIG_PMC_MSP
+               } else if ((iir & UART_IER_BUSY) == UART_IER_BUSY) {

   Hm, masking IIR with IER mask, is this correct? Doubt it.

+                       /*
+                        * The MSP (DesignWare APB UART) serial subsystem has a
+                        * non-standard interrupt condition (0x7) which means
+                        * that the LCR was written while the UART was busy, so
+                        * the LCR was not actually written.  It is cleared by
+                        * reading the special non-standard extended UART status
+                        * register.
+                        */
+                       unsigned int tmp;
+                       if( up->port.line == 0 )
+                               tmp = *UART0_STATUS_REG;
+                       else
+                               tmp = *UART1_STATUS_REG;
+                       
+                       /* Check if saved on LCR write */
+                       if( up->dwapb_lcr != -1 )
+                               serial_outp(up, UART_LCR, up->dwapb_lcr);
+                       else
+                               printk(KERN_ERR "serial8250: UART BUSY, no LCR 
write!\n" );
+
+                       handled = 1;
+                       end = NULL;
+#endif

Not sure if this also shouldn't be handled in other places which check for interrupt status, like serial8250_timeout()...

[...]
Index: linux_2_6/drivers/serial/8250.h
===================================================================
RCS file: linux_2_6/drivers/serial/8250.h,v
retrieving revision 1.1.1.6
retrieving revision 1.4
diff -u -r1.1.1.6 -r1.4
--- linux_2_6/drivers/serial/8250.h     19 Oct 2006 21:00:58 -0000      1.1.1.6
+++ linux_2_6/drivers/serial/8250.h     19 Oct 2006 22:08:15 -0000      1.4
@@ -49,6 +49,7 @@
  #define UART_BUG_QUOT (1 << 0)  /* UART has buggy quot LSB */
  #define UART_BUG_TXEN (1 << 1)  /* UART has buggy TX IIR status */
  #define UART_BUG_NOMSR        (1 << 2)  /* UART has buggy MSR status bits 
(Au1x00) */
+#define UART_BUG_DWTHRE (1 << 3) /* UART has buggy DesignWare THRE interrupt 
re-assertion */

  #define PROBE_RSA     (1 << 0)
  #define PROBE_ANY     (~0)
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
retrieving revision 1.5
diff -u -r1.1.1.7 -r1.5
--- 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       19 Oct 2006 22:08:16 -0000      
1.5
@@ -258,6 +258,8 @@
  #define UPF_CONS_FLOW         ((__force upf_t) (1 << 23))
  #define UPF_SHARE_IRQ         ((__force upf_t) (1 << 24))
  #define UPF_BOOT_AUTOCONF     ((__force upf_t) (1 << 28))
+#define UPF_DW_THRE_BUG                ((__force upf_t)(1 << 29)) /* 
DesignWare THRE hardware BUG

   The need for the new flag seems doubtful to me.

+                                                                               
                                * (cannot be autodetected) */

   The patch is linewrapped

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
retrieving revision 1.3
diff -u -r1.1.1.2 -r1.3
--- 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        19 Oct 2006 19:45:04 -0000      
1.3
@@ -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_IER_BUSY          0x07    /* Busy Detect */

Are you sure it's not *IIR* value? Doesn't look like interrupt mask for IER. And IIR value of 7 already means something else, namely, no interrupt and
receiver status. Hm...

MBR, Sergei

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