From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailout2.w1.samsung.com (mailout2.w1.samsung.com [210.118.77.12]) (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 802381EB1AA for ; Thu, 5 Jun 2025 07:47:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=210.118.77.12 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749109678; cv=none; b=ZikU33xe3DVlIRCB2VC+ITTBPLEQsAQbuXQYPwKd8lBNjNlMSJoOR3H6ybxyQn3IJkNT+tRAjH/mfI+cdGwg1eEcdKbPX0kAgHN18/gOIYSM7A68L5Rq+8xYYIwP6ccgqFKgX71Jcgo10oQWCES81CAJxqHX5PwyDrgGCBk0YxY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749109678; c=relaxed/simple; bh=L4dgUyx5WByKEYS/nMDJHqxiWkX1T8ea8/hUUikNN4Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:From:In-Reply-To: Content-Type:References; b=EJZ32/0hC7JIwczSWvyxIqG4Vcp7n0HhtW59DD4EuPYM8Ji+D2rFPDepPmDcTeGocnO+ok2PYIy1hz7RZ65T79ufoqdp1eI1kf1cgRlB4KFB8nOH3xpgqBbRDRdjhbISEAIqMrSG/MF1A9nGZgaPhla8Lk2nGyttwGj2Avo2oMU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=samsung.com; spf=pass smtp.mailfrom=samsung.com; dkim=pass (1024-bit key) header.d=samsung.com header.i=@samsung.com header.b=Lx8H/eN4; arc=none smtp.client-ip=210.118.77.12 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=samsung.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=samsung.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=samsung.com header.i=@samsung.com header.b="Lx8H/eN4" Received: from eucas1p1.samsung.com (unknown [182.198.249.206]) by mailout2.w1.samsung.com (KnoxPortal) with ESMTP id 20250605074749euoutp0225d319d430c0a708bb3d6e53f683570c~GFfoqq2n42304623046euoutp02D for ; Thu, 5 Jun 2025 07:47:49 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 mailout2.w1.samsung.com 20250605074749euoutp0225d319d430c0a708bb3d6e53f683570c~GFfoqq2n42304623046euoutp02D DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=samsung.com; s=mail20170921; t=1749109669; bh=wQ4r2UrMO9HeWwWj73XcqSp64Ha0LrQiq2rssP1dDuU=; h=Date:Subject:To:Cc:From:In-Reply-To:References:From; b=Lx8H/eN4+gJmiZWwy0JVaKHPIMHJTrPUO9jU9LxlP6rl7YpKSjoSdg3AOmBatrTaN 29+ugSKoTZJxnInwOrCJA4utIS3IGCH2f2lKWmOskNCwRc87PI5Z+8xQI4t9MogBKP txhvt3/SUEbSLW6vwZXDot4dqoHRHCRDGCmPAKuA= Received: from eusmtip2.samsung.com (unknown [203.254.199.222]) by eucas1p2.samsung.com (KnoxPortal) with ESMTPA id 20250605074748eucas1p28e67e82124190453f8cc77872b8ecbb1~GFfn7AmSH2541025410eucas1p2l; Thu, 5 Jun 2025 07:47:48 +0000 (GMT) Received: from [192.168.1.44] (unknown [106.210.136.40]) by eusmtip2.samsung.com (KnoxPortal) with ESMTPA id 20250605074747eusmtip2b9d586a7c9f00d970573a42cf8dd1011~GFfm3yx930322103221eusmtip2A; Thu, 5 Jun 2025 07:47:47 +0000 (GMT) Message-ID: Date: Thu, 5 Jun 2025 09:47:47 +0200 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 3/8] drm/imagination: Use pwrseq for TH1520 GPU power management To: Krzysztof Kozlowski Cc: Drew Fustini , Guo Ren , Fu Wei , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Bartosz Golaszewski , Philipp Zabel , Frank Binns , Matt Coster , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Ulf Hansson , Marek Szyprowski , linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, dri-devel@lists.freedesktop.org Content-Language: en-US From: Michal Wilczynski In-Reply-To: Content-Transfer-Encoding: 7bit X-CMS-MailID: 20250605074748eucas1p28e67e82124190453f8cc77872b8ecbb1 X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-RootMTR: 20250529222405eucas1p18ed1254bf1b2d78468734656fec537e1 X-EPHeader: CA X-CMS-RootMailID: 20250529222405eucas1p18ed1254bf1b2d78468734656fec537e1 References: <20250530-apr_14_for_sending-v3-0-83d5744d997c@samsung.com> <20250530-apr_14_for_sending-v3-3-83d5744d997c@samsung.com> <20250603-whispering-jaybird-of-thunder-f87867@kuoka> On 6/4/25 14:07, Krzysztof Kozlowski wrote: > On 04/06/2025 13:53, Michal Wilczynski wrote: >>>> >>>> The GPU node will depend on the AON node, which will be the sole >>>> provider for the 'gpu-power' sequencer (based on the discussion in patch >>>> 1). >>>> >>>> Therefore, if the AON/pwrseq driver has already completed its probe, and >>>> devm_pwrseq_get() in the GPU driver subsequently returns -EPROBE_DEFER >>>> (because pwrseq_get found 'no match' on the bus for 'gpu-power'), the >>>> interpretation is that the AON driver did not register this optional >>>> sequencer. Since AON is the only anticipated source, it implies the >>>> sequencer won't become available later from its designated provider. >>> >>> I don't understand why you made this assumption. AON could be a module >>> and this driver built-in. AON will likely probe later. >> >> You're absolutely right that AON could be a module and would generally >> probe later in that scenario. However, the GPU device also has a >> 'power-domains = <&aon TH1520_GPU_PD>' dependency. If the AON driver (as >> the PM domain provider) were a late probing module, the GPU driver's >> probe would hit -EPROBE_DEFER when its power domain is requested >> which happens before attempting to get other resources like a power >> sequencer. > > Huh, so basically you imply certain hardware design and certain DTS > description in your driver code. Well, that's clearly fragile design to > me, because you should not rely how hardware properties are presented in > DTS. Will work here on th1520 with this DTS, won't work with something else. > > Especially that this looks like generic Imagination GPU code, common to > multiple devices, not TH1520 only specific. > >> >> So, if the GPU driver's code does reach the devm_pwrseq_get(dev, >> "gpu-power") call, it strongly implies the AON driver has already >> successfully probed. >> >> This leads to the core challenge with the optional 'gpu-power' >> sequencer: Even if the AON driver has already probed, if it then chooses >> not to register the "gpu-power" sequence (because it's an optional >> feature), pwrseq_get() will still find "no device matched" on the >> pwrseq_bus and return EPROBE_DEFER. >> >> If the GPU driver defers here, as it normally should for -EPROBE_DEFER, >> it could wait indefinitely for an optional sequence that its >> already probed AON provider will not supply. >> >> Anyway I think you're right, that this is probably confusing and we >> shouldn't rely on this behavior. >> >> To solve this, and to allow the GPU driver to correctly handle >> -EPROBE_DEFER when a sequencer is genuinely expected, I propose using a >> boolean property on the GPU's DT node, e.g. >> img,gpu-expects-power-sequencer. If the GPU node provides this property >> it means the pwrseq 'gpu-power' is required. > > No, that would be driver design in DTS. > > I think the main problem is the pwrseq API: you should get via phandle, > not name of the pwrseq controller. That's how all producer-consumer > relationships are done in OF platforms. Bart, Given Krzysztof's valid concerns about the current name based lookup in pwrseq_get() and the benefits of phandle based resource linking in OF platforms: Would you be open to a proposal for extending the pwrseq API to allow consumers to obtain a sequencer (or a specific target sequence) via a phandle defined in their Device Tree node? For instance, a consumer device could specify power-sequencer = <&aon> and a new API variant could resolve this. > > It's also fragile to rely on names in case of systems with multiple > similar devices. This does not affect your platform and this hardware in > general, but shows issues with interface: imagine multiple gpus and > multiple pwr sequence devices. Which one should be obtained? > gpu-power-1? But if GPUs are the same class of devices (e.g. 2x TG1520 > GPU) this is just imprecise. > > > Best regards, > Krzysztof > Best regards, -- Michal Wilczynski