From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.codeaurora.org ([198.145.29.96]:47926 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753122AbcLHVQD (ORCPT ); Thu, 8 Dec 2016 16:16:03 -0500 Date: Thu, 8 Dec 2016 13:16:01 -0800 From: Stephen Boyd To: Laurent Pinchart Cc: linux-omap@vger.kernel.org, linux-clk@vger.kernel.org, Paul Walmsley , Tero Kristo , Richard Watts , Tony Lindgren , Alexander Kinzer Subject: Re: [PATCH v3] clk: ti: omap36xx: Work around sprz319 advisory 2.1 Message-ID: <20161208211601.GK5423@codeaurora.org> References: <1480713278-6884-1-git-send-email-laurent.pinchart@ideasonboard.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1480713278-6884-1-git-send-email-laurent.pinchart@ideasonboard.com> Sender: linux-clk-owner@vger.kernel.org List-ID: On 12/02, Laurent Pinchart wrote: > From: Richard Watts > > The OMAP36xx DPLL5, driving EHCI USB, can be subject to a long-term > frequency drift. The frequency drift magnitude depends on the VCO update > rate, which is inversely proportional to the PLL divider. The kernel > DPLL configuration code results in a high value for the divider, leading > to a long term drift high enough to cause USB transmission errors. In > the worst case the USB PHY's ULPI interface can stop responding, > breaking USB operation completely. This manifests itself on the > Beagleboard xM by the LAN9514 reporting 'Cannot enable port 2. Maybe the > cable is bad?' in the kernel log. > > Errata sprz319 advisory 2.1 documents PLL values that minimize the > drift. Use them automatically when DPLL5 is used for USB operation, > which we detect based on the requested clock rate. The clock framework > will still compute the PLL parameters and resulting rate as usual, but > the PLL M and N values will then be overridden. This can result in the > effective clock rate being slightly different than the rate cached by > the clock framework, but won't cause any adverse effect to USB > operation. > > Signed-off-by: Richard Watts > [Upported from v3.2 to v4.9] > Signed-off-by: Laurent Pinchart > --- Applied to clk-next -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project