Re: [PATCH v2] serial: sc16is7xx: fix bug in sc16is7xx_set_baud() when using prescaler

Jiri Slaby
2024-05-02T07:48:31Z

On 30. 04. 24, 22:04, 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>
>
> ---
>
> Changes for V2:
> - Change prescaler type to "unsigned int" (Jiri S.)

Thanks.

Reviewed-by: Jiri Slaby <jirislaby@kernel.org>

--
js
suse labs