linux-kernel - Re: [PATCH v2] serial: sc16is7xx: fix bug in sc16is7xx_set

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Message-ID: <4f960a0b-85f3-403f-b75a-47fb1b4ea6aa@kernel.org>
Date: Thu, 2 May 2024 09:48:27 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Hugo Villeneuve <hugo@...ovil.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jon Ringle <jringle@...dpoint.com>
Cc: Hugo Villeneuve <hvilleneuve@...onoff.com>, stable@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH v2] serial: sc16is7xx: fix bug in sc16is7xx_set_baud()
 when using prescaler

On 30. 04. 24, 22:04, Hugo Villeneuve wrote:
> From: Hugo Villeneuve <hvilleneuve@...onoff.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@...r.kernel.org
> Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
> 
> ---
> 
> Changes for V2:
> - Change prescaler type to "unsigned int" (Jiri S.)

Thanks.

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

-- 
js
suse labs