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=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 759FCC432C3 for ; Thu, 28 Nov 2019 22:20:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 41DE1217D7 for ; Thu, 28 Nov 2019 22:20:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726653AbfK1WUF (ORCPT ); Thu, 28 Nov 2019 17:20:05 -0500 Received: from cloudserver094114.home.pl ([79.96.170.134]:54885 "EHLO cloudserver094114.home.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726569AbfK1WUF (ORCPT ); Thu, 28 Nov 2019 17:20:05 -0500 Received: from 79.184.255.242.ipv4.supernova.orange.pl (79.184.255.242) (HELO kreacher.localnet) by serwer1319399.home.pl (79.96.170.134) with SMTP (IdeaSmtpServer 0.83.320) id eea6408bb1d4e6fd; Thu, 28 Nov 2019 23:20:02 +0100 From: "Rafael J. Wysocki" To: Thierry Reding Cc: "Rafael J. Wysocki" , Len Brown , Pavel Machek , Greg Kroah-Hartman , Dmitry Osipenko , Linux PM , dri-devel , linux-tegra Subject: Re: [PATCH 1/2] PM / runtime: Allow drivers to override runtime PM behaviour on sleep Date: Thu, 28 Nov 2019 23:20:01 +0100 Message-ID: <4149037.GOuMSCS4uT@kreacher> In-Reply-To: <2310325.iNVD75376c@kreacher> References: <20191128160314.2381249-1-thierry.reding@gmail.com> <20191128163623.GA2382107@ulmo> <2310325.iNVD75376c@kreacher> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On Thursday, November 28, 2019 11:03:57 PM CET Rafael J. Wysocki wrote: > On Thursday, November 28, 2019 5:50:26 PM CET Thierry Reding wrote: > > > > --0F1p//8PRICkK4MW > > Content-Type: text/plain; charset=us-ascii > > Content-Disposition: inline > > Content-Transfer-Encoding: quoted-printable > > > > On Thu, Nov 28, 2019 at 05:14:51PM +0100, Rafael J. Wysocki wrote: > > > On Thu, Nov 28, 2019 at 5:03 PM Thierry Reding = > > wrote: > > > > > > > > From: Thierry Reding > > > > > > > > Currently the driver PM core will automatically acquire a runtime PM > > > > reference for devices before system sleep is entered. This is needed > > > > to avoid potential issues related to devices' parents getting put to > > > > runtime suspend at the wrong time and causing problems with their > > > > children. > > >=20 > > > Not only for that. > > >=20 > > > > In some cases drivers are carefully written to avoid such issues and > > > > the default behaviour can be changed to allow runtime PM to operate > > > > regularly during system sleep. > > >=20 > > > But this change breaks quite a few assumptions in the core too, so no, > > > it can't be made. > > > > Anything in particular that I can look at? I'm not seeing any issues > > when I test this, which could of course mean that I'm just getting > > lucky. > > There are races and such that you may never hit during casual testing. > > > One thing that irritated me is that I think this used to work. I do > > recall testing suspend/resume a few years ago and devices would get > > properly runtime suspended/resumed. > > Not true at all. > > The PM core has always taken PM-runtime references on all devices pretty much > since when PM-runtime was introduced. > > > I did some digging but couldn't > > find anything that would have had an impact on this. > > > > Given that this is completely opt-in feature, why are you categorically > > NAK'ing this? > > The general problem is that if any device has been touched by system-wide > suspend code, it should not be subject to PM-runtime any more until the > subsequent system-wide resume is able to undo whatever the suspend did. > > Moreover, if a device is runtime-suspended, the system-wide suspend code > may mishandle it, in general. That's why PM-runtime suspend is not allowed > during system-wide transitions at all. And it has always been like that. > > For a specific platform you may be able to overcome these limitations if > you are careful enough, but certainly they are there in general and surely > you cannot prevent people from using your opt-in just because they think > that they know what they are doing. BTW, what if user space prevents PM-runtime from suspending devices by writing "on" to their "control" files? System-wide suspend is (of course) still expected to work in that case, so how exactly would you overcome that? From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH 1/2] PM / runtime: Allow drivers to override runtime PM behaviour on sleep Date: Thu, 28 Nov 2019 23:20:01 +0100 Message-ID: <4149037.GOuMSCS4uT@kreacher> References: <20191128160314.2381249-1-thierry.reding@gmail.com> <20191128163623.GA2382107@ulmo> <2310325.iNVD75376c@kreacher> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <2310325.iNVD75376c@kreacher> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Thierry Reding Cc: Len Brown , Linux PM , Greg Kroah-Hartman , "Rafael J. Wysocki" , dri-devel , Pavel Machek , linux-tegra , Dmitry Osipenko List-Id: linux-tegra@vger.kernel.org T24gVGh1cnNkYXksIE5vdmVtYmVyIDI4LCAyMDE5IDExOjAzOjU3IFBNIENFVCBSYWZhZWwgSi4g V3lzb2NraSB3cm90ZToKPiBPbiBUaHVyc2RheSwgTm92ZW1iZXIgMjgsIDIwMTkgNTo1MDoyNiBQ TSBDRVQgVGhpZXJyeSBSZWRpbmcgd3JvdGU6Cj4gPiAKPiA+IC0tMEYxcC8vOFBSSUNrSzRNVwo+ ID4gQ29udGVudC1UeXBlOiB0ZXh0L3BsYWluOyBjaGFyc2V0PXVzLWFzY2lpCj4gPiBDb250ZW50 LURpc3Bvc2l0aW9uOiBpbmxpbmUKPiA+IENvbnRlbnQtVHJhbnNmZXItRW5jb2Rpbmc6IHF1b3Rl ZC1wcmludGFibGUKPiA+IAo+ID4gT24gVGh1LCBOb3YgMjgsIDIwMTkgYXQgMDU6MTQ6NTFQTSAr MDEwMCwgUmFmYWVsIEouIFd5c29ja2kgd3JvdGU6Cj4gPiA+IE9uIFRodSwgTm92IDI4LCAyMDE5 IGF0IDU6MDMgUE0gVGhpZXJyeSBSZWRpbmcgPHRoaWVycnkucmVkaW5nQGdtYWlsLmNvbT49Cj4g PiAgd3JvdGU6Cj4gPiA+ID4KPiA+ID4gPiBGcm9tOiBUaGllcnJ5IFJlZGluZyA8dHJlZGluZ0Bu dmlkaWEuY29tPgo+ID4gPiA+Cj4gPiA+ID4gQ3VycmVudGx5IHRoZSBkcml2ZXIgUE0gY29yZSB3 aWxsIGF1dG9tYXRpY2FsbHkgYWNxdWlyZSBhIHJ1bnRpbWUgUE0KPiA+ID4gPiByZWZlcmVuY2Ug Zm9yIGRldmljZXMgYmVmb3JlIHN5c3RlbSBzbGVlcCBpcyBlbnRlcmVkLiBUaGlzIGlzIG5lZWRl ZAo+ID4gPiA+IHRvIGF2b2lkIHBvdGVudGlhbCBpc3N1ZXMgcmVsYXRlZCB0byBkZXZpY2VzJyBw YXJlbnRzIGdldHRpbmcgcHV0IHRvCj4gPiA+ID4gcnVudGltZSBzdXNwZW5kIGF0IHRoZSB3cm9u ZyB0aW1lIGFuZCBjYXVzaW5nIHByb2JsZW1zIHdpdGggdGhlaXIKPiA+ID4gPiBjaGlsZHJlbi4K PiA+ID49MjAKPiA+ID4gTm90IG9ubHkgZm9yIHRoYXQuCj4gPiA+PTIwCj4gPiA+ID4gSW4gc29t ZSBjYXNlcyBkcml2ZXJzIGFyZSBjYXJlZnVsbHkgd3JpdHRlbiB0byBhdm9pZCBzdWNoIGlzc3Vl cyBhbmQKPiA+ID4gPiB0aGUgZGVmYXVsdCBiZWhhdmlvdXIgY2FuIGJlIGNoYW5nZWQgdG8gYWxs b3cgcnVudGltZSBQTSB0byBvcGVyYXRlCj4gPiA+ID4gcmVndWxhcmx5IGR1cmluZyBzeXN0ZW0g c2xlZXAuCj4gPiA+PTIwCj4gPiA+IEJ1dCB0aGlzIGNoYW5nZSBicmVha3MgcXVpdGUgYSBmZXcg YXNzdW1wdGlvbnMgaW4gdGhlIGNvcmUgdG9vLCBzbyBubywKPiA+ID4gaXQgY2FuJ3QgYmUgbWFk ZS4KPiA+IAo+ID4gQW55dGhpbmcgaW4gcGFydGljdWxhciB0aGF0IEkgY2FuIGxvb2sgYXQ/IEkn bSBub3Qgc2VlaW5nIGFueSBpc3N1ZXMKPiA+IHdoZW4gSSB0ZXN0IHRoaXMsIHdoaWNoIGNvdWxk IG9mIGNvdXJzZSBtZWFuIHRoYXQgSSdtIGp1c3QgZ2V0dGluZwo+ID4gbHVja3kuCj4gCj4gVGhl cmUgYXJlIHJhY2VzIGFuZCBzdWNoIHRoYXQgeW91IG1heSBuZXZlciBoaXQgZHVyaW5nIGNhc3Vh bCB0ZXN0aW5nLgo+IAo+ID4gT25lIHRoaW5nIHRoYXQgaXJyaXRhdGVkIG1lIGlzIHRoYXQgSSB0 aGluayB0aGlzIHVzZWQgdG8gd29yay4gSSBkbwo+ID4gcmVjYWxsIHRlc3Rpbmcgc3VzcGVuZC9y ZXN1bWUgYSBmZXcgeWVhcnMgYWdvIGFuZCBkZXZpY2VzIHdvdWxkIGdldAo+ID4gcHJvcGVybHkg cnVudGltZSBzdXNwZW5kZWQvcmVzdW1lZC4KPiAKPiBOb3QgdHJ1ZSBhdCBhbGwuCj4gCj4gVGhl IFBNIGNvcmUgaGFzIGFsd2F5cyB0YWtlbiBQTS1ydW50aW1lIHJlZmVyZW5jZXMgb24gYWxsIGRl dmljZXMgcHJldHR5IG11Y2gKPiBzaW5jZSB3aGVuIFBNLXJ1bnRpbWUgd2FzIGludHJvZHVjZWQu Cj4gCj4gPiBJIGRpZCBzb21lIGRpZ2dpbmcgYnV0IGNvdWxkbid0Cj4gPiBmaW5kIGFueXRoaW5n IHRoYXQgd291bGQgaGF2ZSBoYWQgYW4gaW1wYWN0IG9uIHRoaXMuCj4gPiAKPiA+IEdpdmVuIHRo YXQgdGhpcyBpcyBjb21wbGV0ZWx5IG9wdC1pbiBmZWF0dXJlLCB3aHkgYXJlIHlvdSBjYXRlZ29y aWNhbGx5Cj4gPiBOQUsnaW5nIHRoaXM/Cj4gCj4gVGhlIGdlbmVyYWwgcHJvYmxlbSBpcyB0aGF0 IGlmIGFueSBkZXZpY2UgaGFzIGJlZW4gdG91Y2hlZCBieSBzeXN0ZW0td2lkZQo+IHN1c3BlbmQg Y29kZSwgaXQgc2hvdWxkIG5vdCBiZSBzdWJqZWN0IHRvIFBNLXJ1bnRpbWUgYW55IG1vcmUgdW50 aWwgdGhlCj4gc3Vic2VxdWVudCBzeXN0ZW0td2lkZSByZXN1bWUgaXMgYWJsZSB0byB1bmRvIHdo YXRldmVyIHRoZSBzdXNwZW5kIGRpZC4KPiAKPiBNb3Jlb3ZlciwgaWYgYSBkZXZpY2UgaXMgcnVu dGltZS1zdXNwZW5kZWQsIHRoZSBzeXN0ZW0td2lkZSBzdXNwZW5kIGNvZGUKPiBtYXkgbWlzaGFu ZGxlIGl0LCBpbiBnZW5lcmFsLiAgVGhhdCdzIHdoeSBQTS1ydW50aW1lIHN1c3BlbmQgaXMgbm90 IGFsbG93ZWQKPiBkdXJpbmcgc3lzdGVtLXdpZGUgdHJhbnNpdGlvbnMgYXQgYWxsLiAgQW5kIGl0 IGhhcyBhbHdheXMgYmVlbiBsaWtlIHRoYXQuCj4gCj4gRm9yIGEgc3BlY2lmaWMgcGxhdGZvcm0g eW91IG1heSBiZSBhYmxlIHRvIG92ZXJjb21lIHRoZXNlIGxpbWl0YXRpb25zIGlmCj4geW91IGFy ZSBjYXJlZnVsIGVub3VnaCwgYnV0IGNlcnRhaW5seSB0aGV5IGFyZSB0aGVyZSBpbiBnZW5lcmFs IGFuZCBzdXJlbHkKPiB5b3UgY2Fubm90IHByZXZlbnQgcGVvcGxlIGZyb20gdXNpbmcgeW91ciBv cHQtaW4ganVzdCBiZWNhdXNlIHRoZXkgdGhpbmsKPiB0aGF0IHRoZXkga25vdyB3aGF0IHRoZXkg YXJlIGRvaW5nLgoKQlRXLCB3aGF0IGlmIHVzZXIgc3BhY2UgcHJldmVudHMgUE0tcnVudGltZSBm cm9tIHN1c3BlbmRpbmcgZGV2aWNlcyBieSB3cml0aW5nCiJvbiIgdG8gdGhlaXIgImNvbnRyb2wi IGZpbGVzPwoKU3lzdGVtLXdpZGUgc3VzcGVuZCBpcyAob2YgY291cnNlKSBzdGlsbCBleHBlY3Rl ZCB0byB3b3JrIGluIHRoYXQgY2FzZSwgc28gaG93CmV4YWN0bHkgd291bGQgeW91IG92ZXJjb21l IHRoYXQ/CgoKCl9fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f CmRyaS1kZXZlbCBtYWlsaW5nIGxpc3QKZHJpLWRldmVsQGxpc3RzLmZyZWVkZXNrdG9wLm9yZwpo dHRwczovL2xpc3RzLmZyZWVkZXNrdG9wLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2RyaS1kZXZlbA==