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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_RED 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 E637CC433DB for ; Thu, 7 Jan 2021 13:21:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8BCCA2065E for ; Thu, 7 Jan 2021 13:21:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728424AbhAGNVP (ORCPT ); Thu, 7 Jan 2021 08:21:15 -0500 Received: from mail.kernel.org ([198.145.29.99]:58096 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728128AbhAGNVO (ORCPT ); Thu, 7 Jan 2021 08:21:14 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 90B5C2065E; Thu, 7 Jan 2021 13:20:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1610025634; bh=VJr6FZamdmy1K/mFU31CgN1qGuUyEOLL56Ue/i5GmcU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ThohcnooT8qscZgi1lsumJwGuncTLxh3yt7kyMmUahNJar9yl1Aem9tr1eWhxQ7gj kfbeJ90aIU/LwxRYSZehp9xNtkMYIBdhEiAs+cUr57ZJiOrYx0jG5k5NJh2GMaSfMW 4brjGI0NtCCh1kqqW88m+LyOS0M2Vy+pdoUiPpdA= Date: Thu, 7 Jan 2021 14:21:54 +0100 From: Greg KH To: Prashant Malani Cc: "open list:USB NETWORKING DRIVERS" , Heikki Krogerus , Benson Leung , open list Subject: Re: [PATCH] usb: typec: Send uevent for num_altmodes update Message-ID: References: <20210107034904.4112029-1-pmalani@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 07, 2021 at 11:57:08AM +0100, Greg KH wrote: > On Thu, Jan 07, 2021 at 01:50:53AM -0800, Prashant Malani wrote: > > Hi Greg, > > > > Thanks for taking a look at the patch. > > > > On Thu, Jan 7, 2021 at 1:16 AM Greg KH wrote: > > > > > > On Wed, Jan 06, 2021 at 07:49:04PM -0800, Prashant Malani wrote: > > > > Generate a change uevent when the "number_of_alternate_modes" sysfs file > > > > for partners and plugs is updated by a port driver. > > > > > > > > Cc: Heikki Krogerus > > > > Cc: Benson Leung > > > > Signed-off-by: Prashant Malani > > > > --- > > > > drivers/usb/typec/class.c | 2 ++ > > > > 1 file changed, 2 insertions(+) > > > > > > > > diff --git a/drivers/usb/typec/class.c b/drivers/usb/typec/class.c > > > > index ebfd3113a9a8..8f77669f9cf4 100644 > > > > --- a/drivers/usb/typec/class.c > > > > +++ b/drivers/usb/typec/class.c > > > > @@ -766,6 +766,7 @@ int typec_partner_set_num_altmodes(struct typec_partner *partner, int num_altmod > > > > return ret; > > > > > > > > sysfs_notify(&partner->dev.kobj, NULL, "number_of_alternate_modes"); > > > > + kobject_uevent(&partner->dev.kobj, KOBJ_CHANGE); > > > > > > Shouldn't the sysfs_notify() handle the "something has changed" logic > > > good enough for userspace, as obviously someone is polling on the thing > > > (otherwise we wouldn't be calling sysfs_notify...) > > > > > > The kobject itself hasn't "changed", but rather an individual attribute > > > has changed. We don't want to create uevents for every individual sysfs > > > attribute changing values, do we? > > > > Fair point. I noticed other attributes in this source file use a > > similar approach (sysfs_notify + kobject_uevent) > > and took guidance from there in an attempt to remain consistent > > (though, of course, your point still stands). > > > > I'm guessing it is for processes that rely on udev events > > (subsystem=typec) rather than polling. > > > > > > > > What is preventing a normal "monitor the sysfs file" logic from working > > > here for anyone who wants to know that the alternate modes have changed? > > > > One limitation I can think of is that this sysfs file is hidden till > > it has a valid value (i.e >= 0), so a user-space process might not > > be able to poll on the file till it is visible (I suppose even then > > one could poll on the parent). > > If the file is being added at this point in time, then yes, it is ok to > send a KOBJ_CHANGE event as that is needed. Is that what is happening > here? In looking at the code more, yes, you are right, I'll go queue this up now, thanks. greg k-h