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 E3AC0C6FA86 for ; Mon, 26 Sep 2022 13:27:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234224AbiIZN1K (ORCPT ); Mon, 26 Sep 2022 09:27:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44818 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231727AbiIZN0u (ORCPT ); Mon, 26 Sep 2022 09:26:50 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ADCD5760E0 for ; Mon, 26 Sep 2022 04:51:42 -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 0025460AB8 for ; Mon, 26 Sep 2022 11:50:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5D51EC433D6; Mon, 26 Sep 2022 11:49:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664193002; bh=Z/TIaNKp8bR7xnaGrhBToyQtEOEgcXRRRy1oqGRgqpQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=YkyGBOxAEZe/9QeHc03sk6OKPHMwTaLe4TcqvgcJmQi9hlPGj0WuViQNWksSdtSF6 3Kez+72cB9XlquncxruvRZo4U0i7cjzedys1niSVhs9188UygMVOHw76KTAnQjCnSM OMglBs0HCHLOC3qJhwaScSUcbND4TAKkdhFqVXKJfCYHvkDPsQa3BqD8evgZgp64wo Dwt7dcss32WkuVtQjTYpIMD82STrjqwR5X1WQ51eu+vykhXlGbc7kD0Tb4AgkJc+3i D2eDDgIcXDe1D8CpYGYkiZ6mfwJZY9GtPg2Z2ZL+p65+DgsAtvuR0uGRfDQ9vYBWCL oSSV5iTqutzKw== Date: Mon, 26 Sep 2022 13:49:55 +0200 From: Lorenzo Pieralisi To: Marc Zyngier Cc: Marek =?iso-8859-1?Q?Beh=FAn?= , Lorenzo Pieralisi , Bjorn Helgaas , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , 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 Message-ID: References: <20220818135140.5996-1-kabel@kernel.org> <20220818135140.5996-4-kabel@kernel.org> <87r10al6a0.wl-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87r10al6a0.wl-maz@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Sat, Sep 17, 2022 at 10:05:59AM +0100, Marc Zyngier wrote: > Hi Lorenzo, > > On Fri, 09 Sep 2022 15:57:11 +0100, > Lorenzo Pieralisi wrote: > > > > [+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] > > > > On Thu, Aug 18, 2022 at 03:51:32PM +0200, Marek Behún wrote: > > > From: Pali Rohár > > > > > > Add support for Data Link Layer State Change in the emulated slot > > > registers and hotplug interrupt via the emulated root bridge. > > > > > > This is mainly useful for when an error causes link down event. With > > > this change, drivers can try recovery. > > > > > > Link down state change can be implemented because Aardvark supports Link > > > Down event interrupt. Use it for signaling that Data Link Layer Link is > > > not active anymore via Hot-Plug Interrupt on emulated root bridge. > > > > > > Link up interrupt is not available on Aardvark, but we check for whether > > > link is up in the advk_pcie_link_up() function. By triggering Hot-Plug > > > Interrupt from this function we achieve Link up event, so long as the > > > function is called (which it is after probe and when rescanning). > > > Although it is not ideal, it is better than nothing. > > > > So before even coming to the code review: this patch does two things. > > > > 1) It adds support for handling the Link down state > > 2) It adds some code to emulate a Link-up event > > > > 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. > > > > 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. > > > > 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. > > 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. Right, thanks. > 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). 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 guess this patch could do with being split between handling link > down and link up events, but that's for you to decide. It is fine for me as-is even though its logic could be simplified by the split. Thanks, Lorenzo > Thanks, > > M. > > -- > Without deviation from the norm, progress is not possible. > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel