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smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=tRj9f0pp; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="tRj9f0pp" Received: from [192.168.88.20] (91-156-87-48.elisa-laajakaista.fi [91.156.87.48]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 223CF6B5; Thu, 29 Aug 2024 13:54:03 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1724932444; bh=18MFg0ZU0gWEGTSRmJyGi2UXhCSkBRuo2F5V7lvrFW4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=tRj9f0ppVRM5zv7lpEUb0256T7/Lqiu56m0Jkr5rbA+WvCipDUkeg6EPm9pJp1vcc q0qKU/2mpqC5B68d1d8cx0ayjq7VVlBlq6HRInS+kpLeV2jPimqGQarAk10kfZBa2B P4cQ+UveA0/rE9DuKn2wTwb9s04VKSBOpYIIS4ZM= Message-ID: Date: Thu, 29 Aug 2024 14:55:07 +0300 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 RFC 2/2] pmdomain: ti-sci: Support retaining PD boot time state To: Ulf Hansson , Abel Vesa , Saravana Kannan , Stephen Boyd Cc: Nishanth Menon , Tero Kristo , Santosh Shilimkar , Dave Gerlach , J Keerthy , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Santosh Shilimkar , linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, dri-devel@lists.freedesktop.org, Devarsh Thakkar References: <20240415-ti-sci-pd-v1-0-a0e56b8ad897@ideasonboard.com> <20240415-ti-sci-pd-v1-2-a0e56b8ad897@ideasonboard.com> Content-Language: en-US From: Tomi Valkeinen Autocrypt: addr=tomi.valkeinen@ideasonboard.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Ulf, On 03/05/2024 16:45, Ulf Hansson wrote: > + Abel, Saravanna, Stephen > > On Mon, 15 Apr 2024 at 19:17, Tomi Valkeinen > wrote: >> >> On 15/04/2024 19:00, Tomi Valkeinen wrote: >>> Add a new flag, TI_SCI_PD_KEEP_BOOT_STATE, which can be set in the dts >>> when referring to power domains. When this flag is set, the ti-sci >>> driver will check if the PD is currently enabled in the HW, and if so, >>> set the GENPD_FLAG_ALWAYS_ON flag so that the PD will stay enabled. >>> >>> The main issue I'm trying to solve here is this: >>> >>> If the Display Subsystem (DSS) has been enabled by the bootloader, the >>> related PD has also been enabled in the HW. When the tidss driver >>> probes, the driver framework will automatically enable the PD. While >>> executing the probe function it is very common for the probe to return >>> EPROBE_DEFER, and, in rarer cases, an actual error. When this happens >>> (probe() returns an error), the driver framework will automatically >>> disable the related PD. >>> >>> Powering off the PD while the DSS is enabled and displaying a picture >>> will cause the DSS HW to enter a bad state, from which (afaik) it can't >>> be woken up except with full power-cycle. Trying to access the DSS in >>> this state (e.g. when retrying the probe) will usually cause the board >>> to hang sooner or later. >>> >>> Even if we wouldn't have this board-hangs issue, it's nice to be able to >>> keep the DSS PD enabled: we want to keep the DSS enabled when the >>> bootloader has enabled the screen. If, instead, we disable the PD at the >>> first EPROBE_DEFER, the screen will (probably) go black. >> >> A few things occurred to me. The driver is supposed to clear the >> GENPD_FLAG_ALWAYS_ON when the driver has probed successfully. There are >> two possible issues with that: >> >> - Afaics, there's no API to do that, and currently I just clear the bit >> in genpd->flags. There's a clear race there, so some locking would be >> required. >> >> - This uses the GENPD_FLAG_ALWAYS_ON flag to say "PD is always on, until >> the driver has started". If the PD would have GENPD_FLAG_ALWAYS_ON set >> for other reasons, the driver would still go and clear the flag, which >> might break things. >> >> Also, unrelated to the above and not a problem in practice at the very >> moment, but I think clocks should also be dealt with somehow. Something, >> at early-ish boot stage, should mark the relevant clocks as in use, so >> that there's no chance they would be turned off when the main kernel has >> started (the main display driver is often a module). >> >> It would be nice to deal with all the above in a single place. I wonder >> if the tidss driver itself could somehow be split into two parts, an >> early part that would probe with minimal dependencies, mainly to reserve >> the core resources without doing any kind of DRM init. And a main part >> which would (somehow) finish the initialization at a later point, when >> we have the filesystem (for firmware) and the other bridge/panel drivers >> have probed. >> >> That can be somewhat achieved with simplefb or simpledrm, though, but we >> can't do any TI DSS specific things there, and it also creates a >> requirement to have either of those drivers built-in, and the related DT >> nodes to be added. > > Without going into too much detail, this and similar problems have > been discussed in the past. With the fw_devlink and the ->sync_state() > callback we are getting closer to a solution, but for genpd a solution > is still pending. > > If you want to read up on earlier discussions and join us moving > forward, that would be great. The last attempt for genpd to move this > forward was posted by Abel Vesa: > https://lore.kernel.org/linux-pm/20230621144019.3219858-1-abel.vesa@linaro.org/ > > Beyond that, we have also discussed various solutions at the last LPC > in Richmond. I think the consensus at that point was that Saravana > targeted to post something for clocks - and when that was done, we > should do the similar thing for genpd. Anyway, I have looped them into > this thread, so they can share any updates on their side of the > matter. Do you know if there's been any recent work related to this? I tried to look around on the lists, but nothing caught my eye. Tomi