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 52831C001B2 for ; Thu, 8 Dec 2022 21:06:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229876AbiLHVGh (ORCPT ); Thu, 8 Dec 2022 16:06:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55500 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229885AbiLHVGb (ORCPT ); Thu, 8 Dec 2022 16:06:31 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4F1A755CAB; Thu, 8 Dec 2022 13:06:27 -0800 (PST) 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 DCEE86206C; Thu, 8 Dec 2022 21:06:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A378AC433EF; Thu, 8 Dec 2022 21:06:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1670533586; bh=J4NaD5DiaIrHO6Wu1hSOZE75QqEaTQJzKrEN8RtbCZ0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fx5D9dQKhmKha4DqL4ADNc9N56jaJFC4a0Nav9VsD8KQd98OJHhuzqUkzIcDQrLEa AHi8dWrttK1cGwRkcYhv7geKPay8pRJecRwfc8Ddf9NIcLieKc5IsmVeoKiwoCIwKj ++TFWpeL2+Lt/PA9B/Qw43ZicB8TkCJubzrSVcFoUpJ0hvnRzbY70WOzpuwWSexGtt Yjrotj7A0caG42eBy7j5uhVnZTI1iN/Dyd+SKspNtH9nJM0+SMTAFhOGxfZViTsQaq qb5DsyPkTWjNl7Xcn0eAR3zdgcTmu3scbuF5XkmDx5Mpl6MwfFhAmq/fKxWTyZQqI0 pBngKijQukMBQ== Date: Thu, 8 Dec 2022 15:06:22 -0600 From: Bjorn Andersson To: Ulf Hansson Cc: Akhil P Oommen , freedreno , dri-devel@lists.freedesktop.org, linux-arm-msm@vger.kernel.org, Rob Clark , Stephen Boyd , Dmitry Baryshkov , Philipp Zabel , Douglas Anderson , krzysztof.kozlowski@linaro.org, Abhinav Kumar , Andy Gross , Daniel Vetter , David Airlie , Konrad Dybcio , Krzysztof Kozlowski , Michael Turquette , Rob Herring , Sean Paul , Stephen Boyd , devicetree@vger.kernel.org, linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 0/6] clk/qcom: Support gdsc collapse polling using 'reset' interface Message-ID: <20221208210622.x656vbf7rum5hrl7@builder.lan> References: <1664960824-20951-1-git-send-email-quic_akhilpo@quicinc.com> <20221201225705.46r2m35ketvzipox@builder.lan> <20221207165457.kwdwwiycbwjpogxl@builder.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Thu, Dec 08, 2022 at 02:40:55PM +0100, Ulf Hansson wrote: > On Wed, 7 Dec 2022 at 17:55, Bjorn Andersson wrote: > > > > On Wed, Dec 07, 2022 at 05:00:51PM +0100, Ulf Hansson wrote: > > > On Thu, 1 Dec 2022 at 23:57, Bjorn Andersson wrote: > > > > > > > > On Wed, Oct 05, 2022 at 02:36:58PM +0530, Akhil P Oommen wrote: > > > > > > > > > > > > > @Ulf, Akhil has a power-domain for a piece of hardware which may be > > > > voted active by multiple different subsystems (co-processors/execution > > > > contexts) in the system. > > > > > > > > As such, during the powering down sequence we don't wait for the > > > > power-domain to turn off. But in the event of an error, the recovery > > > > mechanism relies on waiting for the hardware to settle in a powered off > > > > state. > > > > > > > > The proposal here is to use the reset framework to wait for this state > > > > to be reached, before continuing with the recovery mechanism in the > > > > client driver. > > > > > > I tried to review the series (see my other replies), but I am not sure > > > I fully understand the consumer part. > > > > > > More exactly, when and who is going to pull the reset and at what point? > > > > > > > > > > > Given our other discussions on quirky behavior, do you have any > > > > input/suggestions on this? > > > > > > > > > Some clients like adreno gpu driver would like to ensure that its gdsc > > > > > is collapsed at hardware during a gpu reset sequence. This is because it > > > > > has a votable gdsc which could be ON due to a vote from another subsystem > > > > > like tz, hyp etc or due to an internal hardware signal. To allow > > > > > this, gpucc driver can expose an interface to the client driver using > > > > > reset framework. Using this the client driver can trigger a polling within > > > > > the gdsc driver. > > > > > > > > @Akhil, this description is fairly generic. As we've reached the state > > > > where the hardware has settled and we return to the client, what > > > > prevents it from being powered up again? > > > > > > > > Or is it simply a question of it hitting the powered-off state, not > > > > necessarily staying there? > > > > > > Okay, so it's indeed the GPU driver that is going to assert/de-assert > > > the reset at some point. Right? > > > > > > That seems like a reasonable approach to me, even if it's a bit > > > unclear under what conditions that could happen. > > > > > > > Generally the disable-path of the power-domain does not check that the > > power-domain is actually turned off, because the status might indicate > > that the hardware is voting for the power-domain to be on. > > Is there a good reason why the HW needs to vote too, when the GPU > driver is already in control? > > Or perhaps that depends on the running use case? > > > > > As part of the recovery of the GPU after some fatal fault, the GPU > > driver does something which will cause the hardware votes for the > > power-domain to be let go, and then the driver does pm_runtime_put(). > > Okay. That "something", sounds like a device specific setting for the > corresponding gdsc, right? > > So somehow the GPU driver needs to manage that setting, right? > > > > > But in this case the GPU driver wants to ensure that the power-domain is > > actually powered down, before it does pm_runtime_get() again. To ensure > > that the hardware lost its state... > > I see. > > > > > The proposal here is to use a reset to reach into the power-domain > > provider and wait for the hardware to be turned off, before the GPU > > driver attempts turning the power-domain on again. > > > > > > In other words, there is no reset. This is a hack to make a normally > > asynchronous pd.power_off() to be synchronous in this particular case. > > Alright, assuming I understood your clarifications above correctly > (thanks!), I think I have got a much better picture now. > > Rather than abusing the reset interface, I think we should manage this > through the genpd's power on/off notifiers (GENPD_NOTIFY_OFF). The GPU > driver should register its corresponding device for them > (dev_pm_genpd_add_notifier()). > > The trick however, is to make the behaviour of the power-domain for > the gdsc (the genpd->power_off() callback) conditional on whether the > HW is configured to vote or not. If the HW can vote, it should not > poll for the state - and vice versa when the HW can't vote. > Per Akhil's description I misunderstood who the other voters are; but either way it's not the same "HW configured" mechanism as the one we're already discussing. But if we based on similar means could control if the power_off() ops should be blocking, waiting for the status indication to show that the hardware is indeed powered down, I think this would meet the needs. And GENPD_NOTIFY_OFF seems to provide the notification that it was successful (i.e. happened within the timeout etc). > Would this work? > If we can control the behavior of the genpd, I think it would. Thanks, Bjorn