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| author | Maciej W. Rozycki <macro@orcam.me.uk> | 2021-06-10 20:38:34 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-07-14 17:07:41 +0200 |
| commit | 1e8c052902861cadcc3ac39e4800f0ca8f335622 (patch) | |
| tree | fb6e9f262608ba4370b4cde74ca0832eb5cbf094 /drivers/tty | |
| parent | 63432a8b2af244ea9a82652ce5a4a2d3e95883e9 (diff) | |
| download | linux-stable-1e8c052902861cadcc3ac39e4800f0ca8f335622.tar.gz linux-stable-1e8c052902861cadcc3ac39e4800f0ca8f335622.tar.bz2 linux-stable-1e8c052902861cadcc3ac39e4800f0ca8f335622.zip | |
serial: 8250: Actually allow UPF_MAGIC_MULTIPLIER baud rates
[ Upstream commit 78bcae8616ac277d6cb7f38e211493948ed73e30 ]
Support for magic baud rate divisors of 32770 and 32769 used with SMSC
Super I/O chips for extra baud rates of 230400 and 460800 respectively
where base rate is 115200[1] has been added around Linux 2.5.64, which
predates our repo history, but the origin could be identified as commit
2a717aad772f ("Merge with Linux 2.5.64.") with the old MIPS/Linux repo
also at: <git://git.kernel.org/pub/scm/linux/kernel/git/ralf/linux.git>.
Code that is now in `serial8250_do_get_divisor' was added back then to
`serial8250_get_divisor', but that code would only ever trigger if one
of the higher baud rates was actually requested, and that cannot ever
happen, because the earlier call to `serial8250_get_baud_rate' never
returns them. This is because it calls `uart_get_baud_rate' with the
maximum requested being the base rate, that is clk/16 or 115200 for SMSC
chips at their nominal clock rate.
Fix it then and allow UPF_MAGIC_MULTIPLIER baud rates to be selected, by
requesting the maximum baud rate of clk/4 rather than clk/16 if the flag
has been set. Also correct the minimum baud rate, observing that these
ports only support actual (non-magic) divisors of up to 32767 only.
References:
[1] "FDC37M81x, PC98/99 Compliant Enhanced Super I/O Controller with
Keyboard/Mouse Wake-Up", Standard Microsystems Corporation, Rev.
03/27/2000, Table 31 - "Baud Rates", p. 77
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2105190412280.29169@angie.orcam.me.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'drivers/tty')
| -rw-r--r-- | drivers/tty/serial/8250/8250_port.c | 19 |
1 files changed, 16 insertions, 3 deletions
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index fc5ab2032282..ff3f13693def 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2629,6 +2629,21 @@ static unsigned int serial8250_get_baud_rate(struct uart_port *port, struct ktermios *old) { unsigned int tolerance = port->uartclk / 100; + unsigned int min; + unsigned int max; + + /* + * Handle magic divisors for baud rates above baud_base on SMSC + * Super I/O chips. Enable custom rates of clk/4 and clk/8, but + * disable divisor values beyond 32767, which are unavailable. + */ + if (port->flags & UPF_MAGIC_MULTIPLIER) { + min = port->uartclk / 16 / UART_DIV_MAX >> 1; + max = (port->uartclk + tolerance) / 4; + } else { + min = port->uartclk / 16 / UART_DIV_MAX; + max = (port->uartclk + tolerance) / 16; + } /* * Ask the core to calculate the divisor for us. @@ -2636,9 +2651,7 @@ static unsigned int serial8250_get_baud_rate(struct uart_port *port, * slower than nominal still match standard baud rates without * causing transmission errors. */ - return uart_get_baud_rate(port, termios, old, - port->uartclk / 16 / UART_DIV_MAX, - (port->uartclk + tolerance) / 16); + return uart_get_baud_rate(port, termios, old, min, max); } /* |