From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: [PATCH 2.6.23-rc3] pata_pdc2027x: PLL detection fixes Date: Thu, 23 Aug 2007 05:32:24 -0400 Message-ID: <46CD5428.5090003@garzik.org> References: <200708182058.l7IKwrcJ016820@harpo.it.uu.se> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:48533 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761362AbXHWJc0 (ORCPT ); Thu, 23 Aug 2007 05:32:26 -0400 In-Reply-To: <200708182058.l7IKwrcJ016820@harpo.it.uu.se> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Mikael Pettersson Cc: linux-ide@vger.kernel.org, alan@lxorguk.ukuu.org.uk, albertl@mail.com Mikael Pettersson wrote: > Previously I reported that the pata_pdc2027x PLL detection changes > in kernel 2.6.22 broke the driver on my PowerMac: > >> pata_pdc2027x: Invalid PLL input clock 1691742kHz, give up! > > This is followed by a number of errors and speed reduction > steps on the affected ports. > > There are two bugs in pata_pdc2027x's PLL detection code: > > 1. The PLL counter's start value is read before the chip is > put in "test mode". Outside of test mode the counter is > halted, and on the PowerMac the counter is zero because > the chip hasn't been initialised by its BIOS. > > The fix is to move the read of the start value to after > test mode is started, but before the mdelay() in test mode. > This also improves the precision of the PLL detection. > > 2. The code to compute the number of PLL decrements during the > mdelay() in test mode fails to consider that the PLL counter > only is 30 bits wide. If there is a wraparound, it will compute > an incorrect and much too large value. On the PowerMac, the > start count is zero, the end count is a large 30-bit value, so > wraparound occurs and an out of bounds PLL clock is detected. > > The fix is to mask the (start - end) computation to 30 bits. > > While debugging this I also noticed that pdc_read_counter() > reads the two halves of the 30-bit PLL counter as 16-bit values, > and then combines them as if the halves only are 15 bits wide. > To avoid confusion, the halves should be read as 15-bit values. > > This patch implements all three changes. It fixes the PLL detection > failure on my PowerMac, and doesn't cause any regressions on an x86 > with an identical card. > > Signed-off-by: Mikael Pettersson > --- > drivers/ata/pata_pdc2027x.c | 18 +++++++++--------- > 1 files changed, 9 insertions(+), 9 deletions(-) applied