linux-kernel - Re: [PATCH 1/3] PCI: Add helper to check if any of ancestor device support D3cold

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Message-ID: <20230824115656.GW3465@black.fi.intel.com>
Date:   Thu, 24 Aug 2023 14:56:56 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     bhelgaas@...gle.com, koba.ko@...onical.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] PCI: Add helper to check if any of ancestor device
 support D3cold

Hi,

On Thu, Aug 24, 2023 at 12:46:43PM +0800, Kai-Heng Feng wrote:
> In addition to nearest upstream bridge, driver may want to know if the
> entire hierarchy can be powered off to perform different action.
> 
> So walk higher up the hierarchy to find out if any device has valid
> _PR3.

I'm not entirely sure this is good idea. The drivers should expect that
the power will be turned off pretty soon after device enters D3hot. Also
_PR3 is not PCI concept it's ACPI concept so API like this would only
work on systems with ACPI.