From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (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 5CC1F13C836; Fri, 1 Nov 2024 06:46:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730443569; cv=none; b=UBxKx3EMt92S67Jp0WLaQgi4pjWqv82ABDELn+TTSgMxelJtumTPlcvsciYBfiXIckfsB3mwMCBK4pn1m/wWzgfaYfEOhW0h+3tPgM/r3287ni67XcHQlksNfTHG75qRwdzpA/DdcQCaWHKyWovxZPIFdPfbAdHujy7oxqOiM+4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730443569; c=relaxed/simple; bh=7do0ixXu9WwnMA6mTGgu29YbF/UAUoWuDe+jY/qVAl8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fThlE3Y+znaZ1gTstCEgDF44ywvanHkXbvAd/zimwWtw+abObURWm/F7Tj1W02GpmzlQAdQeM22yfQLUlVtJ/al8zGcK9oZX+S1JHoXfgfqemqSLQbmr97Dha5NwibBYZSQ2lYABRITPXjXFkz/hAFdckpCURNBEk5uuo/6OjX4= ARC-Authentication-Results:i=1; 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=A3wQXONe; 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="A3wQXONe" Received: from [192.168.88.20] (91-157-155-49.elisa-laajakaista.fi [91.157.155.49]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 4D08F710; Fri, 1 Nov 2024 07:45:58 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1730443559; bh=7do0ixXu9WwnMA6mTGgu29YbF/UAUoWuDe+jY/qVAl8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=A3wQXONeBC0zXLjIqQQV19uZqNjeY+8D70YmE5ykXAsNQWqVcotvXxiviXVpuNHOv cASky8l0ktBagf07XUSdmoNT3WrqrjhVPVNG6kMr/LBZWr+/z/COgHcs2bfFwRSpEx VtWo+sSZaa558198BvMxVVkcryOGpZmtNB65XjTE= Message-ID: <0741871e-3028-4159-ba1e-96615c045b7b@ideasonboard.com> Date: Fri, 1 Nov 2024 08:46:00 +0200 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] pmdomain: ti-sci: Set PD on/off state according to the HW state To: Ulf Hansson Cc: Kevin Hilman , Nishanth Menon , Tero Kristo , Santosh Shilimkar , linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, vishalm@ti.com, sebin.francis@ti.com, d-gole@ti.com, Devarsh Thakkar , Vignesh Raghavendra References: <20241022-tisci-pd-boot-state-v1-1-849a6384131b@ideasonboard.com> <7hmsilqrw3.fsf@baylibre.com> <0f027b8e-9c41-4754-923b-2a285fb9593a@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, On 31/10/2024 12:25, Ulf Hansson wrote: > On Thu, 31 Oct 2024 at 08:39, Tomi Valkeinen > wrote: >> >> Hi, >> >> On 30/10/2024 22:04, Kevin Hilman wrote: >>> Tomi Valkeinen writes: >>> >>>> At the moment the driver sets the power state of all the PDs it creates >>>> to off, regardless of the actual HW state. This has two drawbacks: >>>> >>>> 1) The kernel cannot disable unused PDs automatically for power saving, >>>> as it thinks they are off already >>>> >>>> 2) A more specific case (but perhaps applicable to other scenarios >>>> also): bootloader enabled splash-screen cannot be kept on the screen. >>>> >>>> The issue in 2) is that the driver framework automatically enables the >>>> device's PD before calling probe() and disables it after the probe(). >>>> This means that when the display subsystem (DSS) driver probes, but e.g. >>>> fails due to deferred probing, the DSS PD gets turned off and the driver >>>> cannot do anything to affect that. >>>> >>>> Solving the 2) requires more changes to actually keep the PD on during >>>> the boot, but a prerequisite for it is to have the correct power state >>>> for the PD. >>>> >>>> The downside with this patch is that it takes time to call the 'is_on' >>>> op, and we need to call it for each PD. In my tests with AM62 SK, using >>>> defconfig, I see an increase from ~3.5ms to ~7ms. However, the added >>>> feature is valuable, so in my opinion it's worth it. >>>> >>>> The performance could probably be improved with a new firmware API which >>>> returns the power states of all the PDs. >>> >>> Agreed. I think we have to pay this performance price for correctness, >>> and we can optimizie it later with improvements to the SCI firmware and >>> a new API. >>> >>>> There's also a related HW issue at play here: if the DSS IP is enabled >>>> and active, and its PD is turned off without first disabling the DSS >>>> display outputs, the DSS IP will hang and causes the kernel to halt if >>>> and when the DSS driver accesses the DSS registers the next time. >>> >>> Ouch. >>> >>>> With the current upstream kernel, with this patch applied, this means >>>> that if the bootloader enables the display, and the DSS driver is >>>> compiled as a module, the kernel will at some point disable unused PDs, >>>> including the DSS PD. When the DSS module is later loaded, it will hang >>>> the kernel. >>>> >>>> The same issue is already there, even without this patch, as the DSS >>>> driver may hit deferred probing, which causes the PD to be turned off, >>>> and leading to kernel halt when the DSS driver is probed again. This >>>> issue has been made quite rare with some arrangements in the DSS >>>> driver's probe, but it's still there. >>>> >>>> So, because of the DSS hang issues, I think this patch is still an RFC. >>> >>> Like you said, I think that DSS hang is an issue independently of this >>> patch, so it shouldn't hold this up IMO. >> >> In current upstream, if the bootloader has enabled the display, we most >> likely won't hit the DSS hang issue as the PD will stay on until the DSS >> driver has had a chance to probe, and the driver takes actions to avoid >> the hang issue. >> >> With this patch applied, the PD may be turned off before the DSS driver >> has had a chance to probe, causing the board to hang when the DSS driver >> probes the first time. >> >> That's why I'm a bit hesitant to apply this. It could mean that for some >> people their board stops booting. >> >> I'm not even sure what would be the perfect fix for this hang problem... >> >> We could have some built-in early boot code which checks if the DSS is >> enabled, and disables it, so that the hang issue won't happen. But >> that's not good if we try to keep the boot splash on the screen until >> the userspace takes over. >> >> Alternatively we could, somehow, mark the DSS powerdomain to be handled >> in a special way: if the PD is enabled at boot time, it will be kept >> enabled until the DSS driver (somehow) changes the PD back to normal >> operation (and if DSS driver is never loaded, PD will stay on). > > This option is kind of what I am working on. Although, the goal is to > keep the code generic, so ideally we should not need any changes in > the DSS driver to make this work. Let's see. If you need someone to do some testing, you know who to ask =). > That said, it sounds like we should defer $subject patch until we have > a solution for the above, right? Yes, I would say so. I'll collect the tags, and will resend this patch (as a non-RFC) when I think it's safe. Thanks for the feedback, Kevin and Ulf. Tomi