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 D36811E47B3; Tue, 16 Sep 2025 09:14:24 +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=1758014066; cv=none; b=PueXl/yRiLgkUDoG5/nMV2ewktCfc/muA23R9asB8THG1USr0joDc4Jq/oYvbVUHBhbVrtoFfTL4oQ9kmg301G7xMWS4K/Xlk1FJR82u9xv+UJgAjl+KEcKCI1lrNmV5f1W7G5U/JTREIFnsSldQtBMqYJbjTElJDhwMFJ3kZoU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758014066; c=relaxed/simple; bh=MUmLjdC6+9Cut1Kj9JY2ktVSjt81KSam9K5LKJOK/E0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=NEjN1iKynIo78sUs36Kda10zot/wA+54HDgUlDMTeARK0daK1t9rNzQ7AJk76X0sQvfv/tfRzFLNdyJ151J/5b/KPRpor+oAfG5zJb2QvCy3RN7uQfEXq4b0tl3UB+jHXs6Bg+iLmSRpXjXVtES7AexSk6sJ67oWO/4/N6khL4g= ARC-Authentication-Results:i=1; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi, On 11/09/2025 17:38, Ulf Hansson wrote: > On Mon, 8 Sept 2025 at 10:35, Tomi Valkeinen > wrote: >> >> 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. >> >> 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. >> >> 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. >> >> With recent change from Ulf (e.g. commit 13a4b7fb6260 ("pmdomain: core: >> Leave powered-on genpds on until late_initcall_sync")), the sync state >> mechanism comes to rescue. It will keep the power domains enabled, until >> the drivers have probed, or the sync-state is triggered via some other >> mechanism (e.g. manually by the boot scripts). >> >> Reviewed-by: Kevin Hilman >> Tested-by: Kevin Hilman >> Signed-off-by: Tomi Valkeinen > > Makes perfect sense to me! Applied for next, thanks! Thanks! I just noticed that the patch was marked RFC. Just for the record, the v1 was RFC, this wasn't. Tomi