From mboxrd@z Thu Jan  1 00:00:00 1970
From: shawn.guo@freescale.com (Shawn Guo)
Date: Mon, 27 Dec 2010 19:49:40 +0800
Subject: [PATCH] ARM: mxs: Change duart device to use amba-pl011
In-Reply-To: <20101222202542.GT14221@pengutronix.de>
References: <1292857064-5032-1-git-send-email-shawn.guo@freescale.com>
	<1292937130-32155-1-git-send-email-shawn.guo@freescale.com>
	<20101222202542.GT14221@pengutronix.de>
Message-ID: <20101227114938.GA13154@freescale.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Hi Uwe,

On Wed, Dec 22, 2010 at 09:25:42PM +0100, Uwe Kleine-K?nig wrote:
> Hello Shawn,
> 
> On Tue, Dec 21, 2010 at 09:12:10PM +0800, Shawn Guo wrote:
> > The mxs duart is actually an amba-pl011 device. This commit changes
> > the duart device code to dynamically allocate amba-pl011 device,
> > so that drivers/serial/amba-pl011.c can be used on mxs.
> I have problems using this.  The problem I found up to now is that
> during probe of the device (triggered by mxs_add_duart ->
> amba_device_register -> amba_put_disable_pclk) the uart clock is
> disabled.  This happens because initially its usage count is 0 but the
> clock is enabled by barebox.  clk_enable doesn't hurt, but in the
> matching clk_disable the usage count drops to zero again and so the
> clock is disabled in hardware.  After that no further outputs can be
> seen.
> 
I did not see this problem. It's true that the clock is turned off
in amba_device_register. But later, the clock will be turned on
again by amba_probe -> amba_get_enable_pclk very soon.

But we should add something like below in mx28_clocks_init to reflect
the clock status and get usecount updated.

	clk_enable(&uart_clk)

I ran into similar problem with fec driver, and would cover that in
fec patch set.

> I assume the machine dies with a circular exception while trying to
> write something out (e.g. that it cannot write to the console :-), but I
> havn't checked that.
> 
> My first try to put an clk_enable(&uart_clk) after it is registered
> didn't help.
> 
> Did you face the same problem?
> 
> Best regards
> Uwe
> 
> -- 
> Pengutronix e.K.                           | Uwe Kleine-K?nig            |
> Industrial Linux Solutions                 | http://www.pengutronix.de/  |
> 

-- 
Regards,
Shawn