linux-kernel - Re: [PATCH] tty/8250_early: Prevent rounding error in uartclk to baud ratio

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Message-ID: <20120928140328.4ff68806@bob.linux.org.uk>
Date:	Fri, 28 Sep 2012 14:03:28 +0100
From:	Alan Cox <alan@...ux.intel.com>
To:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
Cc:	<gregkh@...uxfoundation.org>, <linux-serial@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <Vineet.Gupta1@...opsys.com>
Subject: Re: [PATCH] tty/8250_early: Prevent rounding error in uartclk to
 baud ratio

On Fri, 28 Sep 2012 16:19:08 +0400
Alexey Brodkin <Alexey.Brodkin@...opsys.com> wrote:

> Modify divisor to select the nearest baud rate divider rather than the
> lowest. It minimizes baud rate errors especially on low UART clock
> frequencies.
> 
> For example, if uartclk is 33000000 and baud is 115200 the ratio is
> about 17.9 The current code selects 17 (5% error) but should select 18
> (0.5% error).
> 
> On the same lines as following:
> http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.9-rc3/2.6.9-rc3-mm2/broken-out/serial-pick-nearest-baud-rate-divider.patch
> 
> Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com>

Seems sensible to me.

Acked-by: Alan Cox <alan@...ux.intel.com>
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