linux-kernel - Re: [PATCH 2/3] PCI/ASPM: Ignore L1 PM Substates if device lacks capability

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Date:   Tue, 4 Oct 2022 20:26:53 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org
Cc:     Vidya Sagar <vidyas@...dia.com>,
        "Saheed O . Bolarinwa" <refactormyself@...il.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rajat Jain <rajatja@...gle.com>,
        "Kenneth R . Crudup" <kenny@...ix.com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Abhishek Sahu <abhsahu@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Krishna Thota <kthota@...dia.com>,
        Manikanta Maddireddy <mmaddireddy@...dia.com>,
        Vidya Sagar <sagar.tv@...il.com>, sagupta@...dia.com,
        linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 2/3] PCI/ASPM: Ignore L1 PM Substates if device lacks
 capability



On 10/4/22 7:58 PM, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> 187f91db8237 ("PCI/ASPM: Remove struct aspm_register_info.l1ss_cap")
> inadvertently removed a check for existence of the L1 PM Substates (L1SS)
> Capability before reading it.
> 
> If there is no L1SS Capability, this means we mistakenly read PCI_COMMAND
> and PCI_STATUS (config address 0x04) and interpret that as the PCI_L1SS_CAP
> register, so we may incorrectly configure L1SS.
> 
> Make sure the L1SS Capability exists before trying to read it.
> 
> Fixes: 187f91db8237 ("PCI/ASPM: Remove struct aspm_register_info.l1ss_cap")
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>  drivers/pci/pcie/aspm.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 4535228e4a64..f12d117f44e0 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -560,6 +560,9 @@ static void aspm_l1ss_init(struct pcie_link_state *link)
>  	u32 parent_l1ss_cap, child_l1ss_cap;
>  	u32 parent_l1ss_ctl1 = 0, child_l1ss_ctl1 = 0;
>  
> +	if (!parent->l1ss || !child->l1ss)
> +		return;

I have noticed that l1ss state is initialized in pci_configure_ltr(). I am
wondering whether it is the right place? Are L1SS and LTR related?


> +
>  	/* Setup L1 substate */
>  	pci_read_config_dword(parent, parent->l1ss + PCI_L1SS_CAP,
>  			      &parent_l1ss_cap);

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer