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Date: Wed, 31 May 2017 17:58:08 +0200 From: Stefan Wahren <stefan.wahren@...e.com> To: Stephen Warren <swarren@...dotorg.org>, Phil Elwell <phil@...pberrypi.org> Cc: Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...eaurora.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, linux-rpi-kernel <linux-rpi-kernel@...ts.infradead.org>, linux-clk@...r.kernel.org Subject: Re: CLK_OF_DECLARE advice required Am 31.05.2017 um 17:27 schrieb Stephen Warren: > On 05/30/2017 06:23 AM, Phil Elwell wrote: >> Hi, >> >> I've run into a problem using the fixed-factor clock on Raspberry Pi >> and I'd >> like some advice before I submit a patch. >> >> Some context: the aim is to use a standard UART and some external >> circuitry >> as a MIDI interface. This would be straightforward except that Linux >> doesn't >> recognise the required 31.25KHz as a valid UART baud rate. Rhe >> workaround is >> to declare the UART clock such that the reported rate differs from >> the actual >> rate. If one sets the reported rate to be (actual*38400)/31250 then >> requesting a 38400 baud rate will result in an actual 31250 baud signal. > > This sounds like the wrong approach. Forcing the port to use a > different clock rate than the user requests would prevent anyone from > using that port for its standard purpose; it'd turn what should be a > runtime decision into a compile-time decision. > > Are you sure there's no way to simply select the correct baud rate on > the port? I see plenty of references to configuring custom baud rates > under Linux when I search Google, e.g.: > >> https://stackoverflow.com/questions/12646324/how-to-set-a-custom-baud-rate-on-linux >> > "How to set a custom baud rate on Linux?" > >> https://sourceware.org/ml/libc-help/2009-06/msg00016.html > "Re: Terminal interface and non-standard baudrates" > I remember this gist from Peter Hurley: https://gist.github.com/peterhurley/fbace59b55d87306a5b8
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