linux-kernel - Re: [PATCH v5 0/6] bcm2835: auxiliar device support for spi

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Date:	Thu, 10 Sep 2015 17:57:49 +0200
From:	Martin Sperl <kernel@...tin.sperl.org>
To:	Noralf Trønnes <noralf@...nnes.org>
Cc:	Eric Anholt <eric@...olt.net>,
	Stephen Warren <swarren@...dotorg.org>,
	Lee Jones <lee@...nel.org>,
	Russell King <linux@....linux.org.uk>,
	Mark Brown <broonie@...nel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
	linux-rpi-kernel@...ts.infradead.org, linux-spi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Phil <phil@...pberrypi.org>
Subject: Re: [PATCH v5 0/6] bcm2835: auxiliar device support for spi


> On 10.09.2015, at 17:48, Noralf Trønnes <noralf@...nnes.org> wrote:
> 
> This looks interesting.
> But there's a challenge with the uart1 and the 8250 driver.
> 
> Phil Elwell has this to say:
> This means that that UART1 isn't an exact clone of a 8250 UART.
> In a particular, the clock divisor is calculated differently.
> A standard 8250 derives the baud rate as clock/(divisor16),
> whereas the BCM2835 mini UART uses clock/(divisor8). This means
> that if you want to use the standard driver then you need to lie
> about the clock frequency, providing a value is twice the real
> value, in order for a suitable divisor to be calculated.
> 
> Ref: https://github.com/raspberrypi/linux/pull/1008#issuecomment-139234607
> 
> So either we need a new uart1 driver or a doubled clock freq. somehow.

Found out the same thing and communicated it to Eric - not 
knowing about the different divider…

Martin--
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