From mboxrd@z Thu Jan 1 00:00:00 1970 From: Darren Hart Subject: Re: [PATCH 0/4] pch_uart: Cleanups, board quirks, and user uartclk parameter Date: Wed, 22 Feb 2012 01:55:42 -0800 Message-ID: <4F44BB9E.7060108@linux.intel.com> References: <20120222085830.1ed8c25e@pyramind.ukuu.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mga11.intel.com ([192.55.52.93]:6815 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750788Ab2BVJ4Q (ORCPT ); Wed, 22 Feb 2012 04:56:16 -0500 In-Reply-To: <20120222085830.1ed8c25e@pyramind.ukuu.org.uk> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Alan Cox Cc: Tomoya MORINAGA , Linux Kernel Mailing List , Feng Tang , Greg Kroah-Hartman , Alan Cox , linux-serial@vger.kernel.org On 02/22/2012 12:58 AM, Alan Cox wrote: >>> assume a 192 MHz clock on all boards. The problem with this approac= h is >>> that the CLKCFG register may have been set to something other than = the >>> 192MHz configuration by the firmware. >=20 > So you can use the early PCI hooks or even bash the register directly= in > your early bootup code. You won't be the only early boot console that > does this sort of thing. There are even people bitbanging PCI I=B2C > interfaces at boot time for such purpose. >=20 >> So, I think default uart_clock 192MHz setting is better than Darren'= s opinion. >=20 > It's certainly easier to maintain, but it would be good to know if th= e > setting can be written or retrieved directly in the early console set= up > using the early PCI ops or similar. OK, I'm not opposed to forcing everything to 192MHz, that would clean u= p pch_uart.c quite a bit. I have heard different things about the specification for this chipset. One statement was that 64MHz was the maximum UART clock. Feng suggests that 192MHz is the recommended UART clock. I need to dig up this spec and determine what it actually says. I have V2 with Alan's feedback from 2/4 incorporated, but I'll hold off unless people want to see it now. Seems like it will change a lot if we force 192MHz everywhere. --=20 Darren Hart Intel Open Source Technology Center Yocto Project - Linux Kernel -- To unsubscribe from this list: send the line "unsubscribe linux-serial"= in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html