Messages in this thread | | | Date | Mon, 29 Apr 2024 08:39:22 +0200 | Subject | Re: [PATCH] serial: sc16is7xx: fix bug in sc16is7xx_set_baud() when using prescaler | From | Jiri Slaby <> |
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On 26. 04. 24, 15:59, Hugo Villeneuve wrote: > From: Hugo Villeneuve <hvilleneuve@dimonoff.com> > > When using a high speed clock with a low baud rate, the 4x prescaler is > automatically selected if required. In that case, sc16is7xx_set_baud() > properly configures the chip registers, but returns an incorrect baud > rate by not taking into account the prescaler value. This incorrect baud > rate is then fed to uart_update_timeout(). > > For example, with an input clock of 80MHz, and a selected baud rate of 50, > sc16is7xx_set_baud() will return 200 instead of 50. > > Fix this by first changing the prescaler variable to hold the selected > prescaler value instead of the MCR bitfield. Then properly take into > account the selected prescaler value in the return value computation. > > Also add better documentation about the divisor value computation. > > Fixes: dfeae619d781 ("serial: sc16is7xx") > Cc: stable@vger.kernel.org > Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com> > --- > drivers/tty/serial/sc16is7xx.c | 23 ++++++++++++++++++----- > 1 file changed, 18 insertions(+), 5 deletions(-) > > diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c > index 03cf30e20b75..dcd6c5615401 100644 > --- a/drivers/tty/serial/sc16is7xx.c > +++ b/drivers/tty/serial/sc16is7xx.c > @@ -555,16 +555,28 @@ static bool sc16is7xx_regmap_noinc(struct device *dev, unsigned int reg) > return reg == SC16IS7XX_RHR_REG; > } > > +/* > + * Configure programmable baud rate generator (divisor) according to the > + * desired baud rate. > + * > + * From the datasheet, the divisor is computed according to: > + * > + * XTAL1 input frequency > + * ----------------------- > + * prescaler > + * divisor = --------------------------- > + * baud-rate x sampling-rate > + */ > static int sc16is7xx_set_baud(struct uart_port *port, int baud) > { > struct sc16is7xx_one *one = to_sc16is7xx_one(port, port); > u8 lcr; > - u8 prescaler = 0; > + int prescaler = 1;
Ugh, why do you move to signed arithmetics?
regards, -- js suse labs
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