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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7148FC32771 for ; Mon, 26 Sep 2022 14:25:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234302AbiIZOZM (ORCPT ); Mon, 26 Sep 2022 10:25:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45178 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234311AbiIZOYs (ORCPT ); Mon, 26 Sep 2022 10:24:48 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7C7C0606B1 for ; Mon, 26 Sep 2022 05:35:55 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id D786F60BEF for ; Mon, 26 Sep 2022 12:35:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2DA9AC433C1; Mon, 26 Sep 2022 12:35:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664195754; bh=+7Dy/qBrAbPQ/VnyDF8M/916yD7tx2rsp8x7Rh1LF+M=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=iKD/KaoBjASUcVsppCdsYJd+4o9qIfRvb3ipDeI4T+NiM2GCqdOIRvHF7+IGEjfNx n0p3xrZ44QG2ZVsraKgL7+8Gb+prhshE4kKRCL1Q2gmnKtnOvZaJ6VfZQBKJDq6yb+ tD26heVhEBDEcXxf8X0mbcu+fp9vbAmhMelAEsaJdydw/x9JHGAS2CKX66cEyFk1nE FXZtDFdnzaFYhD4otiMGxg7xejbRGCEBAs2eYcOOuYhr80M4yubGYUvoVzT3SHtvY7 6f0W0tEUjdxDi8byhud/ara485LkikwS6FWkBHgk0sywDurW2m5Z4XNGrtXXRMtInl QI4dtPU4HRElg== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1ocnKx-00CgqY-Tt; Mon, 26 Sep 2022 13:35:52 +0100 Date: Mon, 26 Sep 2022 08:35:51 -0400 Message-ID: <868rm68g9k.wl-maz@kernel.org> From: Marc Zyngier To: Lorenzo Pieralisi Cc: Marek =?UTF-8?B?QmVow7pu?= , Lorenzo Pieralisi , Bjorn Helgaas , Krzysztof =?UTF-8?B?V2lsY3p5xYRza2k=?= , pali@kernel.org, linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, tglx@linutronix.de Subject: Re: [PATCH 03/11] PCI: aardvark: Add support for DLLSC and hotplug interrupt In-Reply-To: References: <20220818135140.5996-1-kabel@kernel.org> <20220818135140.5996-4-kabel@kernel.org> <87r10al6a0.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: lpieralisi@kernel.org, kabel@kernel.org, lorenzo.pieralisi@arm.com, helgaas@kernel.org, kw@linux.com, pali@kernel.org, linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, tglx@linutronix.de X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Mon, 26 Sep 2022 07:49:55 -0400, Lorenzo Pieralisi wrote: >=20 > On Sat, Sep 17, 2022 at 10:05:59AM +0100, Marc Zyngier wrote: > > Hi Lorenzo, > >=20 > > On Fri, 09 Sep 2022 15:57:11 +0100, > > Lorenzo Pieralisi wrote: > > >=20 > > > [+Marc, Thomas - I can't merge this code without them reviewing it, > > > I am not sure at all you can mix the timer/IRQ code the way you do] > > >=20 > > > On Thu, Aug 18, 2022 at 03:51:32PM +0200, Marek Beh=C3=BAn wrote: > > > > From: Pali Roh=C3=A1r > > > >=20 > > > > Add support for Data Link Layer State Change in the emulated slot > > > > registers and hotplug interrupt via the emulated root bridge. > > > >=20 > > > > This is mainly useful for when an error causes link down event. With > > > > this change, drivers can try recovery. > > > >=20 > > > > Link down state change can be implemented because Aardvark supports= Link > > > > Down event interrupt. Use it for signaling that Data Link Layer Lin= k is > > > > not active anymore via Hot-Plug Interrupt on emulated root bridge. > > > >=20 > > > > Link up interrupt is not available on Aardvark, but we check for wh= ether > > > > link is up in the advk_pcie_link_up() function. By triggering Hot-P= lug > > > > Interrupt from this function we achieve Link up event, so long as t= he > > > > function is called (which it is after probe and when rescanning). > > > > Although it is not ideal, it is better than nothing. > > >=20 > > > So before even coming to the code review: this patch does two things. > > >=20 > > > 1) It adds support for handling the Link down state > > > 2) It adds some code to emulate a Link-up event > > >=20 > > > Now, for (2). IIUC you are adding code to make sure that an HP > > > event is triggered if advk_pcie_link_up() is called and it > > > detects a Link-down->Link-up transition, that has to be notified > > > through an HP event. > > >=20 > > > If that's correct, you have to explain to me please what this is > > > actually achieving and a specific scenario where we want this to be > > > implemented, in fine details; then we add it to the commit log. > > >=20 > > > That aside, the interaction of the timer and the IRQ domain code > > > must be reviewed by Marc and Thomas to make sure this is not > > > a gross violation of the respective subsystems usage. > >=20 > > I don't see anything being a "gross violation" here, at least from an > > interrupt subsystem perspective. In a way, this is synthesising an > > interrupt on the back of some other event, and as long as the context > > is somehow appropriate (something that looks like an interrupt when > > pretending there is one), this should be OK. Other subsystems such as > > i2c GPIO expanders do similar things. >=20 > Right, thanks. >=20 > > The one thing I'm dubious about is the frequency of the timer. Asking > > for a poll of the link every jiffy is bound to be expensive, and it > > would be good to relax this as much as possible, specially on low-end > > HW such as this, where every cycle counts. It is always going to be a > > "best effort" thing, and the commit message doesn't say what's the > > actual grace period to handle this (the spec probably has one). >=20 > AFAICS, the code does not poll the link. It sets a timer only if > the link is checked (eg upon PCI bus forced rescan or config access) > the link is up and it was down, to emulate a HP IRQ. I still find the timer frequency pretty high, but surely the authors of the code have worked out that this wasn't a problem. Thanks, M. --=20 Without deviation from the norm, progress is not possible.