Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933010AbaFKQTJ (ORCPT ); Wed, 11 Jun 2014 12:19:09 -0400 Received: from hqemgate15.nvidia.com ([216.228.121.64]:12487 "EHLO hqemgate15.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752143AbaFKQTG (ORCPT ); Wed, 11 Jun 2014 12:19:06 -0400 X-PGP-Universal: processed; by hqnvupgp07.nvidia.com on Wed, 11 Jun 2014 09:10:17 -0700 Date: Wed, 11 Jun 2014 19:19:02 +0300 From: Peter De Schrijver To: Stephen Warren CC: Mikko Perttunen , Russell King , Thierry Reding , "Andrew Morton" , Linus Walleij , Wolfram Sang , "linux-arm-kernel@lists.infradead.org" , "linux-tegra@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v7 3/5] misc: fuse: Add efuse driver for Tegra Message-ID: <20140611161901.GI5961@tbergstrom-lnx.Nvidia.com> References: <1401973754-19701-1-git-send-email-pdeschrijver@nvidia.com> <1401973754-19701-4-git-send-email-pdeschrijver@nvidia.com> <53984FE3.6010509@nvidia.com> <20140611152551.GH5961@tbergstrom-lnx.Nvidia.com> <53987CA4.4040506@wwwdotorg.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <53987CA4.4040506@wwwdotorg.org> X-NVConfidentiality: public User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 11, 2014 at 05:58:28PM +0200, Stephen Warren wrote: > On 06/11/2014 09:25 AM, Peter De Schrijver wrote: > > On Wed, Jun 11, 2014 at 02:47:31PM +0200, Mikko Perttunen wrote: > >> On 05/06/14 16:09, Peter De Schrijver wrote: > >> ... > >>> +int tegra_fuse_readl(u32 offset, u32 *val) > >>> +{ > >>> + if (!fuse_readl) > >>> + return -ENXIO; > >>> + > >>> + *val = fuse_readl(offset); > >>> + > >>> + return 0; > >>> +} > >>> + > >> > >> -EPROBE_DEFER would be a better error value, so that drivers can work > > > > Ok. > > > >> even if they are initially probed before the fuse driver. Of course, if > >> the fuse initialization is moved into machine init then this is a non-issue. > > > > The exported function will always be initialized later because on Tegra20 it > > requires APB DMA to be available. If you read the fuses directly, the system > > sometimes hangs. > > That's not true in the current code. IIRC, the bug was that *if* an APB > DMA access to anything and a CPU access to the fuses happen at the same > time, then there can be a hang. As such, the current fuse code accesses > the fuses directly (without potential for a hang) if the APB DMA driver > is not available, but once the driver becomes available, it reads the > fuses through DMA instead. Does the new code not do that? > I'm not so sure about that. I have seen the hang when dumping all fuses using sysfs in an otherwise idle system booted from initrd. I don't think there should be any APB DMA activity going on then? Cheers, Peter. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/