From: Anton Vorontsov <avorontsov@ru•mvista.com>
To: Laurent Pinchart <laurentp@cse-semaphore•com>
Cc: David Brownell <david-b@pacbell•net>, linuxppc-dev@ozlabs•org
Subject: Re: [RFC] GPIO-based flow control in the cpm_uart driver
Date: Tue, 15 Apr 2008 17:40:07 +0400 [thread overview]
Message-ID: <20080415134007.GA17096@polina.dev.rtsoft.ru> (raw)
In-Reply-To: <200804151522.36884.laurentp@cse-semaphore.com>
On Tue, Apr 15, 2008 at 03:22:33PM +0200, Laurent Pinchart wrote:
> Hi everybody,
>
> I'm implementing flow control and modem control lines support in the cpm_uart
> driver.
>
> The implementation is based on the GPIO lib. Modem control lines are described
> in the device tree as GPIO resources and accessed through the OF GPIO
> bindings. The I/O ports have to be initialized as GPIOs in the
> platform-specific code.
>
> Reading and writing the modem control lines isn't an issue, but activating
> hardware flow control is more complex. The driver needs to turn dedicated
> functions on and off for the RTS and CTS signals, and the GPIO API doesn't
> provide a way to access the PPAR* registers (which does make sense - although
> arguably - as PPAR* control specific functions, not GPIOs).
>
> Hardcoding RTS and CTS lines control in the driver is not an option I want to
> consider. Extending the GPIO API to handled special functions has been nacked
> in the past (see
> http://ozlabs.org/pipermail/linuxppc-dev/2008-February/051241.html). An
> option would be to export gpio_to_chip from drivers/gpio/gpiolib.c and use
> cpm1/2_set_pin in the cpm_uart driver.
Since you have successfuly ported QE USB controller onto CPM USB
hardware, now it's obvious that we will need generic gpio_set_dedicated()
function. So I would rather beg David to accept gpio_set_dedicated()
approach instead of exporting gpio_to_chip(). That way we'll kill two
birds with one stone.
--
Anton Vorontsov
email: cbouatmailru@gmail•com
irc://irc.freenode.net/bd2
next prev parent reply other threads:[~2008-04-15 13:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-04-15 13:22 [RFC] GPIO-based flow control in the cpm_uart driver Laurent Pinchart
2008-04-15 13:40 ` Anton Vorontsov [this message]
2008-04-15 13:47 ` Laurent Pinchart
2008-04-15 14:30 ` Anton Vorontsov
2008-05-20 0:31 ` David Brownell
2008-05-20 13:00 ` Laurent Pinchart
2008-05-20 0:25 ` David Brownell
2008-05-20 12:50 ` Laurent Pinchart
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