From: Stephen Warren <swarren@wwwdotorg.org>
To: Phil Elwell <phil@raspberrypi.org>
Cc: Michael Turquette <mturquette@baylibre.com>,
Stephen Boyd <sboyd@codeaurora.org>,
linux-clk@vger.kernel.org,
linux-rpi-kernel <linux-rpi-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Eric Anholt <eric@anholt.net>
Subject: Re: CLK_OF_DECLARE advice required
Date: Wed, 31 May 2017 09:27:07 -0600 [thread overview]
Message-ID: <8b65e551-e6dd-cf5c-1b22-e1f1a5996d73@wwwdotorg.org> (raw)
In-Reply-To: <ae427c15-330f-6f8d-e2ac-62a8deacbdc5@raspberrypi.org>
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"
next prev parent reply other threads:[~2017-05-31 15:27 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-30 12:23 CLK_OF_DECLARE advice required Phil Elwell
2017-05-31 15:27 ` Stephen Warren [this message]
2017-05-31 15:58 ` Stefan Wahren
2017-05-31 16:28 ` Phil Elwell
2017-05-31 16:47 ` Stephen Warren
2017-06-01 6:39 ` Stephen Boyd
2017-06-01 8:26 ` Phil Elwell
2017-06-02 22:34 ` Stephen Boyd
2017-06-05 16:24 ` Phil Elwell
2017-06-05 20:13 ` Stephen Boyd
2017-06-06 7:22 ` Geert Uytterhoeven
2017-06-06 20:49 ` Stephen Boyd
2017-06-06 8:49 ` Phil Elwell
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