linux-kernel - Re: [PATCH v2 1/1] PCI: pciehp: Skip DLLSC handling if DPC is triggered

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Message-ID: <1069dc19-35ac-be1a-b02a-3815503cb295@kernel.org>
Date:   Thu, 18 Mar 2021 11:35:55 -0400
From:   Sinan Kaya <okaya@...nel.org>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Lukas Wunner <lukas@...ner.de>,
        Sathyanarayanan Kuppuswamy Natarajan 
        <sathyanarayanan.nkuppuswamy@...il.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Keith Busch <kbusch@...nel.org>, knsathya@...nel.org
Subject: Re: [PATCH v2 1/1] PCI: pciehp: Skip DLLSC handling if DPC is
 triggered

On 3/17/2021 4:02 PM, Kuppuswamy, Sathyanarayanan wrote:
> My point is, there is no race in OS handlers (pciehp_ist() vs
> pcie_do_recovery())
>  However, Sinan wrote in
>> 2018 that one of the issues with hotplug versus DPC is that pciehp
>> may turn off slot power and thereby foil DPC recovery.  (Power off =
>> cold reset, whereas DPC recovery = warm reset.)  This can occur
>> as well if DPC is handled by firmware. 

It has been a while...

If I remember correctly, there is no race condition if the platform
handles DPC and HP interrupts on the same MSI vector.

If HP and DPC interrupts are handled as MSI-x interrupts, these can
fire out of order and can cause problems for each one.

I hope it helps.