On Thu, Feb 16, 2012 at 04:57:59PM -0800, Darren Hart wrote:

I'm working on a tunnel creek (atom e6xx + topcliff PCH) development platform
that uses a 48MHz or 64MHz clock to drive the pch_uart. I've found that if I
force the uart_clock to 48MHz (or 64MHz on the latest rev) I can get the kernel
messages and getty on the serial port.

I see that the the CM-iTC board is special-cased to set a 192MHz uart_clock.
This is done in pch_uart.c code, but there is some register manipulation done in
the pch_phub.c driver and I don't understand the connection. How are the two
related?

Is the pch_phub.c register manipulation required for proper related? It seems to
work without touching those registers if I just force the clock.

The device I'm working with is EFI, and the dmi_get_system_info(DMI_BOARD_NAME)
returns "(null)", so I can't use the same test to identify this board. Is there
another common mechanism I might be able to use?

There's no relevant DMI information for the board at all?  What does:
	grep . /sys/class/dmi/id/*
show?

The following patch (by way of example, not meant for inclusion) gets things
working for this particular board with this command line:

console=ttyPCH1,115200 pch_uart.clock_param=48000000

I believe the right thing to do here is to discover a way to identify the board
and special case the clock as is done for the CM-iTC, but I would like to
understand the purpose of the pch_phub register manipulation code. Does this
make sense?

Thanks,

Darren

quoted

From f83fa6cb575844d8e37f136890fe32258eb88dd2 Mon Sep 17 00:00:00 2001

Message-Id: [off-list ref]
From: Darren Hart <redacted>
Date: Wed, 15 Feb 2012 15:44:18 -0800
Subject: [PATCH] pch_uart: Add clock parameter

Allow for the specification of the clock as a module parameter. This is useful
when a board uses a non-standard clock, or when different versions of a board
use different clocks, and that board name or the version are not available to
the kernel.

You also rename base_baud to uart_clock here, so you might want to
mention it in the changelog entry :)

greg k-h