From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-0031df01.pphosted.com (mx0b-0031df01.pphosted.com [205.220.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DDF9E17591; Fri, 16 Feb 2024 08:01:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=205.220.180.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708070473; cv=none; b=M/9WhIoWYbuuxfBE8tAsBtcn5uQ/Ul+sGyGwWDlT0jCD/JJOxFarvvNuYCCTswT035DmAXB/WjjJBeVA62h3sisd+jWjPCKpBcrOZoUvtdWghpPOulaxK0UphY39rLH1Y26EBzEAJISR2OpDC9zIkkXoK0afxoltBf0EIjVPMtk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708070473; c=relaxed/simple; bh=8+sMLiLDtkXguOlgQu12cov7zp0Zkez8ofBb7z/DWFY=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=oDnSIIzqsy7y082pz0uWVWmnXi4WcpzRtDr1/1Fp3tRIsth30nF7xLps3QxilvkPrwNjI8HXCa9WCRVMwgEJtiYIMPIWKsx4ORsO/ePnVZncnwjYMYtutxASdJx/NgaHrvJwgbyXCJ/x4DN+bESw7qK1FClBmjp+X3V2v23o6Ls= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=quicinc.com; spf=pass smtp.mailfrom=quicinc.com; dkim=pass (2048-bit key) header.d=quicinc.com header.i=@quicinc.com header.b=SRDEsoy8; arc=none smtp.client-ip=205.220.180.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=quicinc.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=quicinc.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=quicinc.com header.i=@quicinc.com header.b="SRDEsoy8" Received: from pps.filterd (m0279873.ppops.net [127.0.0.1]) by mx0a-0031df01.pphosted.com (8.17.1.24/8.17.1.24) with ESMTP id 41G59cEB010137; Fri, 16 Feb 2024 08:00:47 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; h= message-id:date:mime-version:subject:to:cc:references:from :in-reply-to:content-type:content-transfer-encoding; s= qcppdkim1; bh=tqBk8G2oArSxqg6+H9dUVqGQk8Y9DebswvmMPbcPGOk=; b=SR DEsoy8PDY255XJK/JQeLSYNTrH9JZr5fGlw4hucQZa4AU9QkoeglwPfDfk3iU0bT 4cRKa5fZhbXztHbadKo7AJVPjWUxS0BOh/A4ddagaQU59xHiWgaRQG5lEZD5qdOP rSJ2fRhYPrzl+DyvLSJnEnoLajg4aMzlmj3//SQJytPCqdKRt10oIS86jLa/v8a8 +mqYiaBCFUbb3SWjDFG5SqMXjnNSrSBsotbk2Pm0+WqEd0bD+5LnEfnlevyIqNXa g6s5xJ/klzb/qxeB8aei1SZYYs+cplI9uvkXSmV6ptXQ9CevCFmjqEtC31lKh/bQ mCh+UhLqKaVBT/XWY+Pw== Received: from nalasppmta04.qualcomm.com (Global_NAT1.qualcomm.com [129.46.96.20]) by mx0a-0031df01.pphosted.com (PPS) with ESMTPS id 3w9fkfb2er-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 16 Feb 2024 08:00:47 +0000 (GMT) Received: from nalasex01a.na.qualcomm.com (nalasex01a.na.qualcomm.com [10.47.209.196]) by NALASPPMTA04.qualcomm.com (8.17.1.5/8.17.1.5) with ESMTPS id 41G80jlG009174 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 16 Feb 2024 08:00:45 GMT Received: from [10.218.5.19] (10.80.80.8) by nalasex01a.na.qualcomm.com (10.47.209.196) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.40; Fri, 16 Feb 2024 00:00:38 -0800 Message-ID: Date: Fri, 16 Feb 2024 13:30:09 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/5] PM: domains: Allow devices attached to genpd to be managed by HW To: Ulf Hansson CC: Bjorn Andersson , Abel Vesa , "Rafael J. Wysocki" , Kevin Hilman , Pavel Machek , Len Brown , "Greg Kroah-Hartman" , Andy Gross , Konrad Dybcio , Michael Turquette , Stephen Boyd , Stanimir Varbanov , Vikash Garodia , Bryan O'Donoghue , Mauro Carvalho Chehab , Taniya Das , Dmitry Baryshkov , , , , , References: <20240122-gdsc-hwctrl-v4-0-9061e8a7aa07@linaro.org> <20240122-gdsc-hwctrl-v4-1-9061e8a7aa07@linaro.org> <87b7967f-d8c4-426e-92ed-5a418c702481@quicinc.com> Content-Language: en-US From: Jagadeesh Kona In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: nasanex01a.na.qualcomm.com (10.52.223.231) To nalasex01a.na.qualcomm.com (10.47.209.196) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-ORIG-GUID: 5dsPSbP5dS2hIh2OMqliEvaHhDJCiW-f X-Proofpoint-GUID: 5dsPSbP5dS2hIh2OMqliEvaHhDJCiW-f X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-02-16_06,2024-02-14_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 malwarescore=0 adultscore=0 lowpriorityscore=0 impostorscore=0 mlxlogscore=999 spamscore=0 bulkscore=0 suspectscore=0 mlxscore=0 phishscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2401310000 definitions=main-2402160064 On 2/15/2024 9:57 PM, Ulf Hansson wrote: > On Wed, 14 Feb 2024 at 05:29, Jagadeesh Kona wrote: >> >> >> >> On 2/13/2024 7:21 PM, Ulf Hansson wrote: >>> On Tue, 13 Feb 2024 at 14:10, Jagadeesh Kona wrote: >>>> >>>> >>>> >>>> On 2/2/2024 5:59 PM, Ulf Hansson wrote: >>>>> On Fri, 2 Feb 2024 at 00:51, Bjorn Andersson wrote: >>>>>> >>>>>> On Wed, Jan 31, 2024 at 01:12:00PM +0100, Ulf Hansson wrote: >>>>>>> On Wed, 31 Jan 2024 at 02:09, Bjorn Andersson wrote: >>>>>>>> >>>>>>>> On Mon, Jan 22, 2024 at 10:47:01AM +0200, Abel Vesa wrote: >>>>>>>>> From: Ulf Hansson >>>>>>>>> >>>>>>>>> Some power-domains may be capable of relying on the HW to control the power >>>>>>>>> for a device that's hooked up to it. Typically, for these kinds of >>>>>>>>> configurations the consumer driver should be able to change the behavior of >>>>>>>>> power domain at runtime, control the power domain in SW mode for certain >>>>>>>>> configurations and handover the control to HW mode for other usecases. >>>>>>>>> >>>>>>>>> To allow a consumer driver to change the behaviour of the PM domain for its >>>>>>>>> device, let's provide a new function, dev_pm_genpd_set_hwmode(). Moreover, >>>>>>>>> let's add a corresponding optional genpd callback, ->set_hwmode_dev(), >>>>>>>>> which the genpd provider should implement if it can support switching >>>>>>>>> between HW controlled mode and SW controlled mode. Similarly, add the >>>>>>>>> dev_pm_genpd_get_hwmode() to allow consumers to read the current mode and >>>>>>>>> its corresponding optional genpd callback, ->get_hwmode_dev(), which the >>>>>>>>> genpd provider can also implement for reading back the mode from the >>>>>>>>> hardware. >>>>>>>>> >>>>>>>>> Signed-off-by: Ulf Hansson >>>>>>>>> Signed-off-by: Abel Vesa >>>>>>>>> Reviewed-by: Dmitry Baryshkov >>>>>>>>> --- >>>>>>>>> drivers/pmdomain/core.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++ >>>>>>>>> include/linux/pm_domain.h | 17 ++++++++++++ >>>>>>>>> 2 files changed, 86 insertions(+) >>>>>>>>> >>>>>>>>> diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c >>>>>>>>> index a1f6cba3ae6c..41b6411d0ef5 100644 >>>>>>>>> --- a/drivers/pmdomain/core.c >>>>>>>>> +++ b/drivers/pmdomain/core.c >>>>>>>>> @@ -548,6 +548,75 @@ void dev_pm_genpd_synced_poweroff(struct device *dev) >>>>>>>>> } >>>>>>>>> EXPORT_SYMBOL_GPL(dev_pm_genpd_synced_poweroff); >>>>>>>>> >>>>>>>>> +/** >>>>>>>>> + * dev_pm_genpd_set_hwmode - Set the HW mode for the device and its PM domain. >>>>>>>> >>>>>>>> This isn't proper kernel-doc >>>>>>> >>>>>>> Sorry, I didn't quite get that. What is wrong? >>>>>>> >>>>>> >>>>>> https://docs.kernel.org/doc-guide/kernel-doc.html#function-documentation >>>>>> says that there should be () after the function name, and below there >>>>>> should be a Return: >>>>> >>>>> Thanks for the pointers! >>>>> >>>>>> >>>>>>>> >>>>>>>>> + * >>>>>>>>> + * @dev: Device for which the HW-mode should be changed. >>>>>>>>> + * @enable: Value to set or unset the HW-mode. >>>>>>>>> + * >>>>>>>>> + * Some PM domains can rely on HW signals to control the power for a device. To >>>>>>>>> + * allow a consumer driver to switch the behaviour for its device in runtime, >>>>>>>>> + * which may be beneficial from a latency or energy point of view, this function >>>>>>>>> + * may be called. >>>>>>>>> + * >>>>>>>>> + * It is assumed that the users guarantee that the genpd wouldn't be detached >>>>>>>>> + * while this routine is getting called. >>>>>>>>> + * >>>>>>>>> + * Returns 0 on success and negative error values on failures. >>>>>>>>> + */ >>>>>>>>> +int dev_pm_genpd_set_hwmode(struct device *dev, bool enable) >>>>>>>>> +{ >>>>>>>>> + struct generic_pm_domain *genpd; >>>>>>>>> + int ret = 0; >>>>>>>>> + >>>>>>>>> + genpd = dev_to_genpd_safe(dev); >>>>>>>>> + if (!genpd) >>>>>>>>> + return -ENODEV; >>>>>>>>> + >>>>>>>>> + if (!genpd->set_hwmode_dev) >>>>>>>>> + return -EOPNOTSUPP; >>>>>>>>> + >>>>>>>>> + genpd_lock(genpd); >>>>>>>>> + >>>>>>>>> + if (dev_gpd_data(dev)->hw_mode == enable) >>>>>>>> >>>>>>>> Between this and the gdsc patch, the hw_mode state might not match the >>>>>>>> hardware state at boot. >>>>>>>> >>>>>>>> With hw_mode defaulting to false, your first dev_pm_genpd_set_hwmode(, >>>>>>>> false) will not bring control to SW - which might be fatal. >>>>>>> >>>>>>> Right, good point. >>>>>>> >>>>>>> I think we have two ways to deal with this: >>>>>>> 1) If the provider is supporting ->get_hwmode_dev(), we can let >>>>>>> genpd_add_device() invoke it to synchronize the state. >>>>>> >>>>>> I'd suggest that we skip the optimization for now and just let the >>>>>> update hit the driver on each call. >>>>> >>>>> Okay. >>>>> >>>>>> >>>>>>> 2) If the provider doesn't support ->get_hwmode_dev() we need to call >>>>>>> ->set_hwmode_dev() to allow an initial state to be set. >>>>>>> >>>>>>> The question is then, if we need to allow ->get_hwmode_dev() to be >>>>>>> optional, if the ->set_hwmode_dev() is supported - or if we can >>>>>>> require it. What's your thoughts around this? >>>>>>> >>>>>> >>>>>> Iiuc this resource can be shared between multiple clients, and we're >>>>>> in either case returning the shared state. That would mean a client >>>>>> acting upon the returned value, is subject to races. >>>>> >>>>> Not sure I understand this, but I also don't have in-depth knowledge >>>>> of how the HW works. >>>>> >>>>> Isn't the HW mode set on a per device basis? >>>>> >>>>>> >>>>>> I'm therefore inclined to say that we shouldn't have a getter, other >>>>>> than for debugging purposes, in which case reading the HW-state or >>>>>> failing would be reasonable outcomes. >>>>> >>>>> If you only want this for debug purposes, it seems better to keep it >>>>> closer to the rpmh code, rather than adding generic callbacks to the >>>>> genpd interface. >>>>> >>>>> So to conclude, you think having a ->set_hwmode_dev() callback should >>>>> be sufficient and no caching of the current state? >>>>> >>>>> Abel, what's your thoughts around this? >>>>> >>>> >>>> We believe it is good to have get_hwmode_dev() callback supported from >>>> GenPD, since if multiple devices share a GenPD, and if one device moves >>>> the GenPD to HW mode, the other device won't be aware of it and second >>>> device's dev_gpd_data(dev)->hw_mode will still be false. >>>> >>>> If we have this dev_pm_genpd_get_hwmode() API supported and if we assign >>>> dev_gpd_data(dev)->hw_mode after getting the mode from get_hwmode_dev() >>>> callback, consumer drivers can use this API to sync the actual HW mode >>>> of the GenPD. >>> >>> Hmm, I thought the HW mode was being set on a per device basis, via >>> its PM domain. Did I get that wrong? >>> >>> Are you saying there could be multiple devices sharing the same PM >>> domain and thus also sharing the same HW mode? In that case, it sure >>> sounds like we have synchronization issues to deal with too. >>> >> >> Sorry my bad, currently we don't have usecase where multiple devices >> sharing the same PM domain that have HW control support, so there is no >> synchronization issue. > > Okay, good! > >> >> But it would be good to have .get_hwmode_dev() callback for consumer >> drivers to query the actual GenPD mode from HW, whenever they require it. > > Okay, no objection from my side. > > Then the final question is if we need a variable to keep a cache of > the current HW mode for each device. Perhaps we should start simple > and just always invoke the callbacks from genpd, what do you think? > Yes, agree, we can remove the variable and just always invoke the callbacks from genpd. But we may need the variable to reflect GenPD mode in debugfs genpd_summary, or need to invoke get callback there as well to get the current mode. Thanks, Jagadeesh > Kind regards > Uffe