* [PATCH] Revert "serial: 8250: Fix reporting real baudrate value in c_ospeed field"
@ 2021-10-07 13:31 Johan Hovold
2021-10-07 14:21 ` Greg Kroah-Hartman
0 siblings, 1 reply; 3+ messages in thread
From: Johan Hovold @ 2021-10-07 13:31 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: Jiri Slaby, linux-serial, linux-kernel, Johan Hovold, Pali Rohár
This reverts commit 32262e2e429cdb31f9e957e997d53458762931b7.
The commit in question claims to determine the inverse of
serial8250_get_divisor() but failed to notice that some drivers override
the default implementation using a get_divisor() callback.
This means that the computed line-speed values can be completely wrong
and results in regular TCSETS requests failing (the incorrect values
would also be passed to any overridden set_divisor() callback).
Similarly, it also failed to honour the old (deprecated) ASYNC_SPD_FLAGS
and would break applications relying on those when re-encoding the
actual line speed.
There are also at least two quirks, UART_BUG_QUOT and an OMAP1510
workaround, which were happily ignored and that are now broken.
Finally, even if the offending commit were to be implemented correctly,
this is a new feature and not something which should be backported to
stable.
Cc: Pali Rohár <pali@kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
drivers/tty/serial/8250/8250_port.c | 17 -----------------
1 file changed, 17 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index dc6900b2daa8..66374704747e 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2584,19 +2584,6 @@ static unsigned int serial8250_get_divisor(struct uart_port *port,
return serial8250_do_get_divisor(port, baud, frac);
}
-static unsigned int serial8250_compute_baud_rate(struct uart_port *port,
- unsigned int quot)
-{
- if ((port->flags & UPF_MAGIC_MULTIPLIER) && quot == 0x8001)
- return port->uartclk / 4;
- else if ((port->flags & UPF_MAGIC_MULTIPLIER) && quot == 0x8002)
- return port->uartclk / 8;
- else if (port->type == PORT_NPCM)
- return DIV_ROUND_CLOSEST(port->uartclk - 2 * (quot + 2), 16 * (quot + 2));
- else
- return DIV_ROUND_CLOSEST(port->uartclk, 16 * quot);
-}
-
static unsigned char serial8250_compute_lcr(struct uart_8250_port *up,
tcflag_t c_cflag)
{
@@ -2727,14 +2714,11 @@ void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk)
baud = serial8250_get_baud_rate(port, termios, NULL);
quot = serial8250_get_divisor(port, baud, &frac);
- baud = serial8250_compute_baud_rate(port, quot);
serial8250_rpm_get(up);
spin_lock_irqsave(&port->lock, flags);
uart_update_timeout(port, termios->c_cflag, baud);
- if (tty_termios_baud_rate(termios))
- tty_termios_encode_baud_rate(termios, baud, baud);
serial8250_set_divisor(port, baud, quot, frac);
serial_port_out(port, UART_LCR, up->lcr);
@@ -2766,7 +2750,6 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
baud = serial8250_get_baud_rate(port, termios, old);
quot = serial8250_get_divisor(port, baud, &frac);
- baud = serial8250_compute_baud_rate(port, quot);
/*
* Ok, we're now changing the port state. Do it with
--
2.32.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] Revert "serial: 8250: Fix reporting real baudrate value in c_ospeed field"
2021-10-07 13:31 [PATCH] Revert "serial: 8250: Fix reporting real baudrate value in c_ospeed field" Johan Hovold
@ 2021-10-07 14:21 ` Greg Kroah-Hartman
2021-10-07 14:40 ` Pali Rohár
0 siblings, 1 reply; 3+ messages in thread
From: Greg Kroah-Hartman @ 2021-10-07 14:21 UTC (permalink / raw)
To: Johan Hovold; +Cc: Jiri Slaby, linux-serial, linux-kernel, Pali Rohár
On Thu, Oct 07, 2021 at 03:31:46PM +0200, Johan Hovold wrote:
> This reverts commit 32262e2e429cdb31f9e957e997d53458762931b7.
>
> The commit in question claims to determine the inverse of
> serial8250_get_divisor() but failed to notice that some drivers override
> the default implementation using a get_divisor() callback.
>
> This means that the computed line-speed values can be completely wrong
> and results in regular TCSETS requests failing (the incorrect values
> would also be passed to any overridden set_divisor() callback).
>
> Similarly, it also failed to honour the old (deprecated) ASYNC_SPD_FLAGS
> and would break applications relying on those when re-encoding the
> actual line speed.
>
> There are also at least two quirks, UART_BUG_QUOT and an OMAP1510
> workaround, which were happily ignored and that are now broken.
>
> Finally, even if the offending commit were to be implemented correctly,
> this is a new feature and not something which should be backported to
> stable.
>
> Cc: Pali Rohár <pali@kernel.org>
> Signed-off-by: Johan Hovold <johan@kernel.org>
> ---
> drivers/tty/serial/8250/8250_port.c | 17 -----------------
> 1 file changed, 17 deletions(-)
Argh, sorry I missed this, good catch. I'll go queue this up now,
thanks.
greg k-h
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] Revert "serial: 8250: Fix reporting real baudrate value in c_ospeed field"
2021-10-07 14:21 ` Greg Kroah-Hartman
@ 2021-10-07 14:40 ` Pali Rohár
0 siblings, 0 replies; 3+ messages in thread
From: Pali Rohár @ 2021-10-07 14:40 UTC (permalink / raw)
To: Greg Kroah-Hartman; +Cc: Johan Hovold, Jiri Slaby, linux-serial, linux-kernel
On Thursday 07 October 2021 16:21:30 Greg Kroah-Hartman wrote:
> On Thu, Oct 07, 2021 at 03:31:46PM +0200, Johan Hovold wrote:
> > This reverts commit 32262e2e429cdb31f9e957e997d53458762931b7.
> >
> > The commit in question claims to determine the inverse of
> > serial8250_get_divisor() but failed to notice that some drivers override
> > the default implementation using a get_divisor() callback.
> >
> > This means that the computed line-speed values can be completely wrong
> > and results in regular TCSETS requests failing (the incorrect values
> > would also be passed to any overridden set_divisor() callback).
> >
> > Similarly, it also failed to honour the old (deprecated) ASYNC_SPD_FLAGS
> > and would break applications relying on those when re-encoding the
> > actual line speed.
> >
> > There are also at least two quirks, UART_BUG_QUOT and an OMAP1510
> > workaround, which were happily ignored and that are now broken.
> >
> > Finally, even if the offending commit were to be implemented correctly,
> > this is a new feature and not something which should be backported to
> > stable.
> >
> > Cc: Pali Rohár <pali@kernel.org>
> > Signed-off-by: Johan Hovold <johan@kernel.org>
> > ---
> > drivers/tty/serial/8250/8250_port.c | 17 -----------------
> > 1 file changed, 17 deletions(-)
>
> Argh, sorry I missed this, good catch. I'll go queue this up now,
> thanks.
>
> greg k-h
I was waiting for a reply in discussion for this patch...
https://lore.kernel.org/linux-serial/20210927093704.19768-1-pali@kernel.org/t/#u
There was no reply, so I was surprised it was taken without any
reaction. I was really in impression that patch is waiting.
So sorry for that.
Johan, could you write comments below original patch, so discussion is
not on two places? I would really like to fix this issue because
c_ospeed contains incorrect value.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-10-07 14:40 UTC | newest]
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2021-10-07 13:31 [PATCH] Revert "serial: 8250: Fix reporting real baudrate value in c_ospeed field" Johan Hovold
2021-10-07 14:21 ` Greg Kroah-Hartman
2021-10-07 14:40 ` Pali Rohár
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