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

To: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Subject: Re: [PATCH] serial driver PMC MSP71xx, kernel linux-mips.git mast er
From: Marc St-Jean <Marc_St-Jean@pmc-sierra.com>
Date: Thu, 25 Jan 2007 15:10:17 -0800
Cc: linux-mips@linux-mips.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
User-agent: Thunderbird 1.5.0.9 (X11/20061206)
Sergei Shtylyov wrote:
> 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... :-/

I see that but was under the impression cvs diff did that so all lines
lineup correctly whether they have a +, -, or neither. It doesn't affect
applying the patches for me, did you try?


>  >   {
>  > +     /* Save the offset before it's remapped */
>  > +     int save_offset = offset;
> 
>     Is there real need to save this? What regshift equals for this UART?

Yes, we have a regshift of 2 on this SoC and it could be different on other
SoCs which reuse the UART IP.


>  >       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...

It's just a dummy read to ensure that any writes which clear interrupts have
reached the device before returning from the IRQ.


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

OK, moved onto 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?

Good point. I didn't write that one and assumed reading the IIR was part of the 
fix.
It just tested fine without it so it's gone.


>  > @@ -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. :-)

Our regshift is definitely 2 on this SoC and we don't have any problems with
console output before the serial driver opens. So assuming it's using
8250_early.c for initial console output I can only conclude that it works
because UART_TX is offset 0 and the port was left configured from our
ROM monitor.


>  > 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

I have it, I forgot to respin against the master.


> 
>  > 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... :-)

OK, I picked 'data'.


>  > 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.

Will do. I noticed that the other non-standard value UART_IIR_TOD 0x08 is with
the Xscale stuff so I followed suit.

Marc

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