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Date: Fri, 26 Jan 2007 16:28:13 -0800
From: Marc St-Jean <Marc_St-Jean@...-sierra.com>
To: Sergei Shtylyov <sshtylyov@...mvista.com>
Cc: linux-mips@...ux-mips.org, linux-serial@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial driver PMC MSP71xx, kernel linux-mips.git mast
er
Sergei Shtylyov wrote:
> Hello.
>
> Marc St-Jean wrote:
>
> >> > 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.
>
> Yes. And your mailer has probably added another space to lines already
> begginign with space. Some mailers tend to do it, don't know sure why...
> :-/
I'll look into it for the next patch.
> > It doesn't affect applying the patches for me, did you try?
>
> I hadn't but I had no doubts it'll fail... just tried, not a single
> hunk
> applied. :-]
>
> >> > {
> >> > + /* 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.
>
> Agreed then (though still seems avoidable).
>
> >> > 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.
>
> Hm, isn't it CPU write buffer flush? Shouldn't this be handled more
> generically?
No because this peripheral is across an internal SoC bus. Only a read
accessing it will ensure the write is complete. We must insure the
interrupt source is cleared to avoid spurious interrupts.
> [...]
> >> > 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
>
> It comes into action only if you specify console=uart,... kernel option
> for the eraly console support. The "plain" 8250 console driver is
> containded
> within 8250.c itself.
>
> > because UART_TX is offset 0 and the port was left configured from our
> > ROM monitor.
>
> Well, this part of the patch can't be considered complete then (how LSR
> polling is going to work?), so should either be removed or the proper
> regshift
> support added.
Since we don't require it I will drop the 8250_early.c changes from the patch.
I've tested the "mm tree" patch for the backup timer and it works, although
the output seems a little choppy at times. I'll drop the UART_BUG_DWTHRE flag
and associated code.
Marc
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