Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758161Ab2HINGP (ORCPT ); Thu, 9 Aug 2012 09:06:15 -0400 Received: from cantor2.suse.de ([195.135.220.15]:55760 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757998Ab2HINGN (ORCPT ); Thu, 9 Aug 2012 09:06:13 -0400 Date: Thu, 09 Aug 2012 15:06:11 +0200 Message-ID: From: Takashi Iwai To: Thierry Reding Cc: Jaroslav Kysela , David Henningsson , alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] ALSA: hda - Defer probe when loading patch firmware In-Reply-To: <20120809124904.GA830@avionic-0098.mockup.avionic-design.de> References: <1344494723-6827-1-git-send-email-thierry.reding@avionic-design.de> <20120809070813.GA6979@avionic-0098.mockup.avionic-design.de> <20120809073642.GA24695@avionic-0098.mockup.avionic-design.de> <20120809080713.GC24808@avionic-0098.mockup.avionic-design.de> <20120809103430.GA1560@avionic-0098.mockup.avionic-design.de> <20120809124904.GA830@avionic-0098.mockup.avionic-design.de> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/24.1 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7114 Lines: 145 At Thu, 9 Aug 2012 14:49:04 +0200, Thierry Reding wrote: > > On Thu, Aug 09, 2012 at 02:32:38PM +0200, Takashi Iwai wrote: > > At Thu, 9 Aug 2012 12:34:30 +0200, > > Thierry Reding wrote: > > > > > > On Thu, Aug 09, 2012 at 10:21:15AM +0200, Takashi Iwai wrote: > > > > At Thu, 9 Aug 2012 10:07:13 +0200, > > > > Thierry Reding wrote: > > > > > > > > > > On Thu, Aug 09, 2012 at 09:42:48AM +0200, Takashi Iwai wrote: > > > > > > At Thu, 9 Aug 2012 09:36:42 +0200, > > > > > > Thierry Reding wrote: > > > > > > > > > > > > > > On Thu, Aug 09, 2012 at 09:31:30AM +0200, Takashi Iwai wrote: > > > > > > > > At Thu, 9 Aug 2012 09:08:13 +0200, > > > > > > > > Thierry Reding wrote: > > > > > > > > > > > > > > > > > > On Thu, Aug 09, 2012 at 08:57:13AM +0200, Takashi Iwai wrote: > > > > > > > > > > At Thu, 9 Aug 2012 08:45:23 +0200, > > > > > > > > > > Thierry Reding wrote: > > > > > > > > > > > > > > > > > > > > > > Recent changes to the firmware loading helpers cause drivers to stall > > > > > > > > > > > when firmware is loaded during the module_init() call. The snd-hda-intel > > > > > > > > > > > module requests firmware if the patch= parameter is used to load a patch > > > > > > > > > > > file. This patch works around the problem by deferring the probe in such > > > > > > > > > > > cases, which will cause the module to load successfully and the driver > > > > > > > > > > > binding to the device outside the module_init() call. > > > > > > > > > > > > > > > > > > > > Is the "recent" change meant 3.6 kernel, or in linux-next? > > > > > > > > > > > > > > > > > > > > In anyway, I don't understand why such a change was allowed. Most > > > > > > > > > > drivers do call request_firmware() at the device probing time. > > > > > > > > > > If this really has to be resolved in the driver side, it must be a bug > > > > > > > > > > in the firmware loader core code. > > > > > > > > > > > > > > > > > > A good explanation of the problem and subsequent discussion can be found > > > > > > > > > here: > > > > > > > > > > > > > > > > > > http://article.gmane.org/gmane.linux.drivers.video-input-infrastructure/49975 > > > > > > > > > > > > > > > > Yeah, but it doesn't justify this ugly module option. > > > > > > > > It's a simple bug. Papering over it with this option doesn't fix > > > > > > > > anything. > > > > > > > > > > > > > > It's not an option, all it does is defer probing if and only if the > > > > > > > patch parameter was specified to make sure the firmware load won't > > > > > > > stall. I realize that this may not be an optimal solution, but at least > > > > > > > it fixes the problem with no fallout. > > > > > > > > > > > > Ah sorry, I misread the patch. > > > > > > > > > > > > Then it shouldn't be checked at that point. Since 3.5 kernel, the > > > > > > probing code was already split for vga_switcheroo support. > > > > > > > > > > Yes, I saw that. But unless you actually use vga_switcheroo, the second > > > > > stage, azx_probe_continue(), will still be called from azx_probe() and > > > > > therefore ultimately from module_init(). > > > > > > > > Yeah, but this could be easily delayed. The split was already done, > > > > so the next step would be to return after the first half at probe, > > > > then call the second half later. > > > > > > > > > Before coming up with this patch I actually did play around a bit with > > > > > using the asynchronous firmware load functions but it turned out to be > > > > > rather difficult to do so I opted for the easy way. The biggest problem > > > > > I faced was that since patch loading needs to be done very early on, a > > > > > lot of the initialization would need to be done after .probe() and many > > > > > things could still fail, so cleaning up after errors would become > > > > > increasingly difficult. > > > > > > > > async probe is also on my TODO list, but it's deferred ;) > > > > > > > > > > The point you added is the second stage. > > > > > > > > > > I don't understand this sentence. > > > > > > > > I meant that your patch added the check at the second-half probing > > > > function (azx_probe_contine()). That is, it could be already the > > > > point triggered by vga_switcheroo handler, not via module_init any > > > > longer. > > > > > > > > So, after rethinking what you suggested, I wrote a quick patch below. > > > > Could you check whether this works? > > > > > > It oopses, though I can't quite tell where. I need to test some more > > > later to see where it goes wrong. > > > > Yeah, I tested it here and noticed, too. As mentioned, the behavior > > of -EPROBE_DEFER is somehow flaky. For example, when it's used for > > modules, the deferred probe will be never triggered (unless a new > > device is bound). > > Yes, the idea is that probing is only retried after other drivers have > bound to other devices because otherwise nothing about any missing > resources can have changed. This however would indicate that deferred > probing is not the right solution here, after all we're not waiting for > another resource to become available. Something like delayed work might > be better suited. > > Well, asynchronous firmware load is actually the right solution, delayed > work just might be a better workaround. =) > > For completeness I should say that I've been using deferred probing with > modules quite successfully on another platform, so it is not a general > problem. Rather as you said, it is only triggered if another module is > loaded after the deferral. Yes. But if you reload just snd-hda-intel module, it'll be stuck. > > Considering the problem again, it's currently an issue only for the > > built-in sound driver, right? AFAIK, request_firmware() works fine > > for modules. If so, a simple "fix" to avoid the unexpected behavior > > is to make CONFIG_SND_HDA_PATCH_LOADER depending on CONFIG_SND_HDA=m. > > It'd be simple enough for merging 3.6 kernel. > > I've actually seen this problem with snd-hda-intel built as a module as > well, so I don't think this kind of temporary fix will do. Hmm, for modules, request_firmware() seems working fine on my systems, no matter whether it succeeds or not. Could you double-check? If the user-helper isn't ready at module loading time, of course, it stalls, just like the kernel driver. But it should be available there. > > I almost finished writing the patch to use request_firmware_nowait() > > version, but I'm afraid it's too intrusive for 3.6. If disabling the > > patch loader for the built-in driver is OK, I'd queue the > > request_firmware_nowait() patches to 3.7 queue. > > I'm in no hurry, and the patch that I carry works for me. If there are > no other reasons to pull a corresponding fix into 3.6 I can certainly > wait for 3.7. The particular setup that I have requires other patches > that may not go into 3.6 anyway. OK. Takashi -- 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/