[PATCH 0/4] bcm2835: enable auxiliary uart1

Eric Anholt eric at anholt.net
Mon Sep 14 07:53:16 PDT 2015

kernel at martin.sperl.org writes:

> From: Martin Sperl <kernel at martin.sperl.org>
> The bcm2835 SOC contains an auxiliary uart, which is very close
> to the ns16550 with some differences.
> The big difference is that the uart HW is not using an internal divider
> of 16 but 8, which results in an effictive baud-rate being twice
> the requested baud-rate.
> The bcm2835-aux-uart is also special in such that it is enabled/disabled
> by a gate in the clock, which is managed by the clk-bcm2835-aux
> clock driver.
> there are 2 options:
> * defining the clock-frequency property in the device tree to 500k
>   instead of 250k, but this keeps the HW block disabled making the
>   uart not work.
> * defining a clock in the device tree, but this results in a baud rate
>   that is twice the requested baud-rate.
> To address this this patch-set introduce a new property in the device tree
> to define a clock divider other than 16.
> This currently just scales the clock by a factor of 16/divider.
> Note that the use of fixed-factor-clock has also been proposed as a
> workarround, but this does not really describe the hw in the device tree
> so another solution was needed that allows a correct representation of
> the HW in the device tree.

I personally lean toward the fixed-factor-clock solution, but could go
either way.  Serial maintainers, what do you think?
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