From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 92708C43382 for ; Tue, 25 Sep 2018 14:00:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 40EF620877 for ; Tue, 25 Sep 2018 14:00:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 40EF620877 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=st.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729339AbeIYUHz (ORCPT ); Tue, 25 Sep 2018 16:07:55 -0400 Received: from mx08-00178001.pphosted.com ([91.207.212.93]:35461 "EHLO mx07-00178001.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727165AbeIYUHy (ORCPT ); Tue, 25 Sep 2018 16:07:54 -0400 Received: from pps.filterd (m0046661.ppops.net [127.0.0.1]) by mx08-.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id w8PDwwqD018241; Tue, 25 Sep 2018 15:59:29 +0200 Received: from beta.dmz-eu.st.com (beta.dmz-eu.st.com [164.129.1.35]) by mx08-00178001.pphosted.com with ESMTP id 2mncme9bbh-1 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT); Tue, 25 Sep 2018 15:59:29 +0200 Received: from zeta.dmz-eu.st.com (zeta.dmz-eu.st.com [164.129.230.9]) by beta.dmz-eu.st.com (STMicroelectronics) with ESMTP id D0B973A; Tue, 25 Sep 2018 13:59:28 +0000 (GMT) Received: from Webmail-eu.st.com (sfhdag5node3.st.com [10.75.127.15]) by zeta.dmz-eu.st.com (STMicroelectronics) with ESMTP id 98EC251A5; Tue, 25 Sep 2018 13:59:28 +0000 (GMT) Received: from [10.48.0.167] (10.75.127.44) by SFHDAG5NODE3.st.com (10.75.127.15) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Tue, 25 Sep 2018 15:59:27 +0200 Subject: Re: [RESEND PATCH] Revert "pwm: Set class for exported channels in sysfs" From: Fabrice Gasnier To: Thierry Reding CC: , , , , , , , , , , References: <1537538567-5377-1-git-send-email-fabrice.gasnier@st.com> <20180924115301.GV21032@ulmo> <20180924142318.GG23547@ulmo> Message-ID: <4278fef9-ec60-239a-dd0a-29a89d742fa4@st.com> Date: Tue, 25 Sep 2018 15:59:26 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.75.127.44] X-ClientProxiedBy: SFHDAG8NODE2.st.com (10.75.127.23) To SFHDAG5NODE3.st.com (10.75.127.15) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-09-25_08:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/24/2018 05:50 PM, Fabrice Gasnier wrote: > On 09/24/2018 04:23 PM, Thierry Reding wrote: >> On Mon, Sep 24, 2018 at 03:59:03PM +0200, Fabrice Gasnier wrote: >>> On 09/24/2018 01:53 PM, Thierry Reding wrote: >>>> On Fri, Sep 21, 2018 at 04:02:47PM +0200, Fabrice Gasnier wrote: >>>>> This reverts commit 7e5d1fd75c3dde9fc10c4472b9368089d1b81d00 as it causes >>>>> regression with multiple pwm chip. It creates a new entry in >>>>> '/sys/class/pwm' every time a 'pwmX' is exported with 'echo X > export': >>>>> - 1st time export will create an entry in /sys/class/pwm/pwmX >>>>> - when another export happens on another pwmchip, it can't be created >>>>> (e.g. -EEXIST) >>>>> >>>>> This also changes existing ABI (Documentation/ABI/testing/sysfs-class-pwm): >>>>> - pmwX should be there: /sys/class/pwm/pwmchipN/pwmX >>>>> >>>>> Example on stm32 (stm32429i-eval) platform: >>>>> $ ls /sys/class/pwm >>>>> pwmchip0 pwmchip4 >>>>> >>>>> $ cd /sys/class/pwm/pwmchip0/ >>>>> $ echo 0 > export >>>>> $ ls /sys/class/pwm >>>>> pwm0 pwmchip0 pwmchip4 >>>>> >>>>> $ cd /sys/class/pwm/pwmchip4/ >>>>> $ echo 0 > export >>>>> sysfs: cannot create duplicate filename '/class/pwm/pwm0' >>>>> ...Exception stack follows... >>>>> >>>>> Signed-off-by: Fabrice Gasnier >>>>> --- >>>>> drivers/pwm/sysfs.c | 1 - >>>>> 1 file changed, 1 deletion(-) >>>> >>>> Can we come up with an alternative that allows us to have both? We want >>>> uevent and proper sysfs creation, or is that not possible? >>> >>> Hi Thierry, all, >>> >>> With current approach: >>> - "export->child.class = parent->class" >>> - ABI (e.g. "pwm%d") device name isn't unique with multiple pwm chip. >>> I think this is not possible. >>> >>> Trying to think of an alternative... I just did a quick test, by >>> changing device name, to take pwmchip into account: >>> + export->child.class = parent->class; >>> export->child.release = pwm_export_release; >>> export->child.parent = parent; >>> export->child.devt = MKDEV(0, 0); >>> export->child.groups = pwm_groups; >>> - dev_set_name(&export->child, "pwm%u", pwm->hwpwm); >>> + dev_set_name(&export->child, "pwmchip%d-pwm%u", chip->base, >>> pwm->hwpwm); >>> >>> But this also impacts existing ABI :-( >>> Would you have suggestions to send an uevent, without modifying ABI ? >> >> I don't quite understand why, in the example you show in the commit >> message, the pwmX nodes appear in the top-level /sys/class/pwm >> directory. According to Documentation/ABI/testing/sysfs-class-pwm they >> should appear as /sys/class/pwm/pwmchipN/pwmX. I can only imagine that >> setting the class may have changed that. > > Yes, adding the class makes the link to be created under /sys/class/pwm: > device_register() -> device_add() -> device_add_class_symlinks() > In device_add_class_symlinks(): > ... > if (!dev->class) > return 0; > ... > /* link in the class directory pointing to the device */ > error = sysfs_create_link(&dev->class->p->subsys.kobj, > &dev->kobj, dev_name(dev)); > ... > >> If so, perhaps we can >> workaround that by creating a new class that is not parent->class? Hi Thierry, Maybe there's a way around, keeping the revert patch, without impacting the ABI: - pwmX cannot be added to pwm/another class without issue as discussed (numbering isn't unique). - pwmchipN already belongs to pwm class. I did some testing, trying to send uevent on the pwmX directly, without success: uevents are filtered as pwmX doesn't belong to a class. Still, it is possible to send uevent (KOBJ_CHANGE) on pwmchipN device, to notify of a change, e.g. pwmX channel being exported/unexported. I run following prototype (with revert patch). static int pwm_export_child(struct device *parent, struct pwm_device *pwm) { + char *pwm_prop[2]; struct pwm_export *export; int ret; ... kfree(export); return ret; } + pwm_prop[0] = kasprintf(GFP_KERNEL, "EXPORT=pwm%u", pwm->hwpwm); + pwm_prop[1] = NULL; + kobject_uevent_env(&parent->kobj, KOBJ_CHANGE, pwm_prop); + kfree(pwm_prop[0]); return 0; } static int pwm_unexport_child(struct device *parent, struct pwm_device *pwm) { struct device *child; + char *pwm_prop[2]; if (!test_and_clear_bit(PWMF_EXPORTED, &pwm->flags)) return -ENODEV; ... if (!child) return -ENODEV; + pwm_prop[0] = kasprintf(GFP_KERNEL, "UNEXPORT=pwm%u", pwm->hwpwm); + pwm_prop[1] = NULL; + kobject_uevent_env(&parent->kobj, KOBJ_CHANGE, pwm_prop); + kfree(pwm_prop[0]); + /* for device_find_child() */ Then, I run a quick test: # udevadm monitor --environment & # echo 0 > /sys/class/pwm/pwmchip0/export KERNEL[197.321736] change /devices/.../pwm/pwmchip0 (pwm) ACTION=change DEVPATH=/devices/.../pwm/pwmchip0 EXPORT=pwm0 SEQNUM=2045 SUBSYSTEM=pwm # echo 0 > /sys/class/pwm/pwmchip4/export KERNEL[202.089676] change /devices/.../pwm/pwmchip4 (pwm) ACTION=change DEVPATH=/devices/.../pwm/pwmchip4 EXPORT=pwm0 SEQNUM=2046 SUBSYSTEM=pwm Also unexport will report change events to userland: # echo 0 > /sys/class/pwm/pwmchip0/unexport KERNEL[1691.112765] change /devices/.../pwm/pwmchip0 (pwm) ACTION=change DEVPATH=/devices/.../pwm/pwmchip0 SEQNUM=2047 SUBSYSTEM=pwm UNEXPORT=pwm0 Do you think this may be a way around? Please let me know if this may satisfy need for uevents. Best regards, Fabrice > > And this link is added using dev_name(). So I doubt adding a new class > will change the current behavior. > >> >> Thierry >>