From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCH v7 3/5] misc: fuse: Add efuse driver for Tegra Date: Wed, 11 Jun 2014 09:58:28 -0600 Message-ID: <53987CA4.4040506@wwwdotorg.org> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140611152551.GH5961@tbergstrom-lnx.Nvidia.com> Sender: linux-kernel-owner@vger.kernel.org To: Peter De Schrijver , Mikko Perttunen Cc: 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" List-Id: linux-tegra@vger.kernel.org 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? From mboxrd@z Thu Jan 1 00:00:00 1970 From: swarren@wwwdotorg.org (Stephen Warren) Date: Wed, 11 Jun 2014 09:58:28 -0600 Subject: [PATCH v7 3/5] misc: fuse: Add efuse driver for Tegra In-Reply-To: <20140611152551.GH5961@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> Message-ID: <53987CA4.4040506@wwwdotorg.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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?