linux-kernel - Re: [PATCH v2] serial: 8250_dw: Improve unwritable LCR workaround

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Message-ID: <20131128194720.GD13182@localhost>
Date:	Thu, 28 Nov 2013 16:47:21 -0300
From:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	Tim Kryger <tim.kryger@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	linux-serial@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Patch Tracking <patches@...aro.org>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Lior Amsalem <alior@...vell.com>,
	Jason Cooper <jason@...edaemon.net>,
	ARM Kernel List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] serial: 8250_dw: Improve unwritable LCR workaround

Hi Thomas, Tim:

On Thu, Nov 28, 2013 at 09:30:34AM +0100, Thomas Petazzoni wrote:
> Dear Ezequiel Garcia,
> 
> On Wed, 27 Nov 2013 15:54:49 -0300, Ezequiel Garcia wrote:
> 
> > > An external device may be keeping the UART busy and preventing LCR
> > > from being written.
> > > 
> > > What device is attached to ttyS1?
> > 
> > There's no device attached at ttyS1. I've just tested this in another
> > box and it seems the same error is obtained on each unused port:
> 
> Are you sure about this? I suppose you're testing on the Armada XP GP
> board, and this board has a 4 ports FTDI chip, and according to the
> board schematics the four UARTs are all connected to the FTDI chip. So
> from the SoC perspective, ttyS1 is connected to something, as far as I
> can understand. Or maybe you also tested Armada XP DB ?
> 

Yeah, sorry about that. I missed the FTDI chip. As Thomas says the XP GP
board I'm testing this on, has its four UARTs connected to a FTDI chip.

Changing the console port by setting "console=ttyS1,115200" gives this:

[..]
Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
dw-apb-uart d0012000.serial: Couldn't set LCR to 191
dw-apb-uart d0012000.serial: Couldn't set LCR to 191
dw-apb-uart d0012000.serial: Couldn't set LCR to 224
dw-apb-uart d0012000.serial: Couldn't set LCR to 224
d0012000.serial: ttyS0 at MMIO 0xd0012000 (irq = 17, base_baud = 15625000) is a 16550A
dw-apb-uart d0012100.serial: Couldn't set LCR to 191
dw-apb-uart d0012100.serial: Couldn't set LCR to 191
dw-apb-uart d0012100.serial: Couldn't set LCR to 224
dw-apb-uart d0012100.serial: Couldn't set LCR to 224
d0012100.serial: ttyS1 at MMIO 0xd0012100 (irq = 18, base_baud = 15625000) is a 16550A
console [ttyS1] enabled
dw-apb-uart d0012200.serial: Couldn't set LCR to 191
dw-apb-uart d0012200.serial: Couldn't set LCR to 191
dw-apb-uart d0012200.serial: Couldn't set LCR to 224
dw-apb-uart d0012200.serial: Couldn't set LCR to 224
d0012200.serial: ttyS2 at MMIO 0xd0012200 (irq = 31, base_baud = 15625000) is a 16550A
dw-apb-uart d0012300.serial: Couldn't set LCR to 191
dw-apb-uart d0012300.serial: Couldn't set LCR to 191
dw-apb-uart d0012300.serial: Couldn't set LCR to 224
dw-apb-uart d0012300.serial: Couldn't set LCR to 224
d0012300.serial: ttyS3 at MMIO 0xd0012300 (irq = 32, base_baud = 15625000) is a 16550A

So we get the "Couldn't set" message in all four ports.

Tim: Any ideas?
-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com
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