From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from bh-25.webhostbox.net ([208.91.199.152]:57077 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751013AbcGRN3d (ORCPT ); Mon, 18 Jul 2016 09:29:33 -0400 Subject: Re: [v2,1/4] hwmon: iio_hwmon: defer probe when no channel is found To: Maxime Ripard References: <1468576754-3273-2-git-send-email-quentin.schulz@free-electrons.com> <20160716170013.GA27490@roeck-us.net> <20160718100232.GE4199@lukather> Cc: Quentin Schulz , jdelvare@suse.com, jic23@kernel.org, knaack.h@gmx.de, lars@metafoo.de, pmeerw@pmeerw.net, wens@csie.org, lee.jones@linaro.org, linux-kernel@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-iio@vger.kernel.org, linux-arm-kernel@lists.infradead.org, thomas.petazzoni@free-electrons.com, antoine.tenart@free-electrons.com From: Guenter Roeck Message-ID: <578CD99E.5000406@roeck-us.net> Date: Mon, 18 Jul 2016 06:29:02 -0700 MIME-Version: 1.0 In-Reply-To: <20160718100232.GE4199@lukather> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-hwmon-owner@vger.kernel.org List-Id: linux-hwmon@vger.kernel.org On 07/18/2016 03:02 AM, Maxime Ripard wrote: > Hi Guenter, > > On Sat, Jul 16, 2016 at 10:00:13AM -0700, Guenter Roeck wrote: >> On Fri, Jul 15, 2016 at 11:59:11AM +0200, Quentin Schulz wrote: >>> iio_channel_get_all returns -ENODEV when it cannot find either phandles and >>> properties in the Device Tree or channels whose consumer_dev_name matches >>> iio_hwmon in iio_map_list. The iio_map_list is filled in by iio drivers >>> which might be probed after iio_hwmon. >>> >>> It is better to defer the probe of iio_hwmon if such error is returned by >>> iio_channel_get_all in order to let a chance to iio drivers to expose >>> channels in iio_map_list. >>> >>> Signed-off-by: Quentin Schulz >>> --- >>> >>> No modifications for this patch since we did not settled for a solution. >>> What should we do? >>> >> AFAICS the only thing we can do is to replace module_platform_driver() with >> its explicitly coded variant, and to use use late_initcall() instead of >> module_init(). > > I thought this kind of changes to the driver init time were > discouraged these days? > Blindly converting -ENODEV to -EPROBEDEFER doesn't sound like a good idea either. >> Anything else would result in endless probe deferrals if there are >> no channels. > > Well, technically, not endless. AFAIK, the kernel only retries when a > new driver is probed, which should hopefully settle down rather > quickly. > Plus each time a new driver is loaded for whatever reason. Also, are you sure that leaving a device in deferred probe state doesn't have undesirable side effects ? For example, would driver_probe_done() ever return true ? Guenter