linux-kernel - Re: [PATCH v4 2/2] PCI: Don't assume root ports from

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Date:   Thu, 25 May 2023 09:03:01 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Mario Limonciello <mario.limonciello@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        S-k Shyam-sundar <Shyam-sundar.S-k@....com>,
        Natikar Basavaraj <Basavaraj.Natikar@....com>,
        Deucher Alexander <Alexander.Deucher@....com>,
        linux-pm@...r.kernel.org, Lukas Wunner <lukas@...ner.de>,
        Iain Lane <iain@...ngesquash.org.uk>
Subject: Re: [PATCH v4 2/2] PCI: Don't assume root ports from > 2015 are power
 manageable



On 5/24/23 12:07 PM, Mario Limonciello wrote:

This looks like a generic fix to me. So why talk about > 2015? IMO,
you can remove > 2015 from the title.

> Using a USB keyboard or mouse to wakeup the system from s2idle fails when
> that XHCI device is connected to a USB-C port for an AMD USB4 router.
> 
> Due to commit 9d26d3a8f1b0 ("PCI: Put PCIe ports into D3 during suspend")
> all PCIe ports go into D3 during s2idle.
> 
> When specific root ports are put into D3 over s2idle on some AMD platforms
> it is not possible for the platform to properly identify wakeup sources.
> This happens whether the root port goes into D3hot or D3cold.

I think Linux/Windows comparison is also not needed. But it is up to you.

> 
> Comparing registers between Linux and Windows 11 this behavior to put
> these specific root ports into D3 at suspend is unique to Linux. On an
> affected system Windows does not put those specific root ports into D3
> over Modern Standby.
> 
> Windows doesn't put the root ports into D3 because root ports are not
> power manageable.
> 
> Linux shouldn't assume root ports support D3 just because they're on a
> machine newer than 2015, the ports should also be deemed power manageable.
> Add an extra check explicitly for root ports to ensure D3 isn't selected
> for these ports.
> 

Other than above suggestions, rest looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>

> Fixes: 9d26d3a8f1b0 ("PCI: Put PCIe ports into D3 during suspend")
> Reported-by: Iain Lane <iain@...ngesquash.org.uk>
> Closes: https://forums.lenovo.com/t5/Ubuntu/Z13-can-t-resume-from-suspend-with-external-USB-keyboard/m-p/5217121
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
> v3->v4:
>  * Move after refactor
> ---
>  drivers/pci/pci.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index d1fa040bcea7..d293db963327 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3015,6 +3015,14 @@ bool pci_bridge_d3_possible(struct pci_dev *bridge)
>  	if (dmi_check_system(bridge_d3_blacklist))
>  		return false;
>  
> +	/*
> +	 * It's not safe to put root ports that don't support power
> +	 * management into D3.
> +	 */
> +	if (pci_pcie_type(bridge) == PCI_EXP_TYPE_ROOT_PORT &&
> +	    !platform_pci_power_manageable(bridge))
> +		return false;
> +
>  	/*
>  	 * It should be safe to put PCIe ports from 2015 or newer
>  	 * to D3.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer