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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C00AD107BCD3 for ; Fri, 13 Mar 2026 17:37:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=1LhKsghhAsGvoVOXQCLsE3fhe8keUmeEp2cUbaI42vI=; b=g5zQ0iZA6xainF+wBvMTgE73n0 OEbqUE6wn96WpAbPQ9dPV898EJbWwMk1URkQEZc8EifQUbIqN3s/4iA4CsV4WNGHTD139IiW3NrYy 8WUXmZ/GFyJ2zbB+noV9quCKYnFvyA0MtPx0mKy02KbTCRDHc929YKPPaYS1YepI/n+AU2Wea1+EM 1DU61LANuKHDqylb1sDya8QvIFbWSCtqprGslD9CL+6gXSxU/iyRV2rXMsjfD9EbShXkRKHlRvp97 jlnQewUMvtAG2mnsgko/p3waOqU+nCJhQhvIve/FCYWWT7Iop/KCqtDGA9Dpx9Rx1ceVLpJ43k/fQ wD9AyMpw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1w16Rh-00000000lu5-0xLA; Fri, 13 Mar 2026 17:37:09 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1w16Rc-00000000ltc-381h; Fri, 13 Mar 2026 17:37:08 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 82FC4176A; Fri, 13 Mar 2026 10:36:55 -0700 (PDT) Received: from [10.57.59.200] (unknown [10.57.59.200]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8E8C03F73B; Fri, 13 Mar 2026 10:36:58 -0700 (PDT) Message-ID: <4f9fdfc9-f2ad-49b1-a6b9-ae64aaa47cfd@arm.com> Date: Fri, 13 Mar 2026 17:36:56 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] PCI: dw-rockchip: Enable async probe by default To: Danilo Krummrich Cc: Manivannan Sadhasivam , Manivannan Sadhasivam , Lorenzo Pieralisi , =?UTF-8?Q?Krzysztof_Wilczy=C5=84ski?= , Rob Herring , Bjorn Helgaas , Heiko Stuebner , Niklas Cassel , Shawn Lin , Hans Zhang <18255117159@163.com>, Nicolas Frattaroli , Wilfred Mallawa , linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org, Anand Moon , Grimmauld , Greg Kroah-Hartman , "Rafael J. Wysocki" , driver-core@lists.linux.dev, Lukas Wunner References: <20260226101032.1042-1-linux.amoon@gmail.com> <177260693908.10259.13055467642416391434.b4-ty@kernel.org> <87bc37ee-234c-4568-b72e-955c130a6838@arm.com> <5d88fb5b-e771-4ea6-8d2c-c5cfd21e5860@arm.com> <55c28218-1638-4b90-a9cd-a177fb5abcb6@arm.com> <6cfe4bda-036f-4bb9-8a08-ed75f61cae24@arm.com> From: Robin Murphy Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260313_103704_882038_8FBB9FD2 X-CRM114-Status: GOOD ( 31.67 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2026-03-13 2:39 pm, Danilo Krummrich wrote: > On Fri Mar 13, 2026 at 2:15 PM CET, Robin Murphy wrote: >> On 2026-03-12 12:59 pm, Danilo Krummrich wrote: >>> On Thu Mar 12, 2026 at 1:48 PM CET, Robin Murphy wrote: >>>> On 2026-03-11 9:09 pm, Danilo Krummrich wrote: >>>>> From a driver-core perspective I think we're rather limited on what we can do; >>>>> we are already in async context at this point and can't magically go back to >>>>> initcall context. >>>>> >>>>> So, the only thing I can think of is to kick off work on a workqueue, which in >>>>> the end would be the same as the deferred probe handling. >>>> >>>> Hmm, in fact, isn't the deferred probe mechanism itself actually quite >>>> appropriate? >>> >>> Yes, I've also mentioned this in [1], including the fact that it technically >>> even complies with the guarantees given by PROBE_FORCE_SYNCHRONOUS. I.e. the >>> documentation says: >>> >>> Use this to annotate drivers that need their probe routines to run >>> synchronously with driver and device registration (with the exception of >>> -EPROBE_DEFER handling - re-probing always ends up being done >>> asynchronously). >>> >>> However, I'm still not sure how I feel about this, since I consider this to be >>> more like a workaround that just moves things to a "more approprite" async >>> context. >> >> I guess the underlying problem there is that there are at least 3 >> different significant aspects to what "synchronous" can mean: >> >> - literally in the context or device/driver registration as documented. >> Off-hand I'm not really sure what useful property may be *specific* to >> those conditions that a driver might rely on, other than for >> super-special cases like platform_driver_probe(). > > I'm not worried about this one, as it is already special by not being compatible > with deferred probe. I.e. the caller already has to promise that the > corresponding probe() call will never return -EPROBE_DEFER. > > This is a much more error prone requirement than just "don't call this from > async" already. > >> - serialised, i.e. probes of multiple devices won't happen concurrently >> on multiple threads. This is probably the one hiding the most driver >> bugs, e.g. internal shared/global state without sufficient >> synchronisation. I guess this falls out as a side-effect of the first >> condition, but AFAICS it *can* also still provided by deferred probe >> (given that it's a single work item iterating a list one-by-one) >> >> - in some regular thread context that isn't liable to have issues >> synchronising against other async_func workers (i.e. the request_module >> case). Again, deferred can't have a problem here, or it wouldn't have >> worked properly in general for the last decade. >> >> So it's not that we'd be relying on some dubious "deferred is always >> synchronous" assumption - AFAICS deferred *can* launch async if the >> driver permits it - more just ratifying that deferred is still able to >> effectively honour all the useful properties of PROBE_FORCE_SYNCHRONOUS >> other than "during registration of the thing". > > Yes, and as mentioned above, EPROBE_DEFER has always been a valid path for > PROBE_FORCE_SYNCHRONOUS, which is why I brought it up as a a workaround in the > first place. > > (The reason why I still say "workaround" is because nothing actually needs to be > deferred.) > > Anyways, as I mentioned... > >>> On the other hand, eventually we want everything to work with >>> PROBE_PREFER_ASYNCHRONOUS, so maybe it's also good enough for the time being. > > ...plus there are not a lot of PROBE_FORCE_SYNCHRONOUS left anyways. > > Do you want to send a patch? Sure, I just wanted to check that you didn't see anything obviously wrong with my reasoning-by-inspection - if you're sufficiently happy then I'll write this up as a proper commit message and post the patch (likely on Monday now) so we can all nit-pick the details :) Cheers, Robin.