Re: [PATCH] PCI: Add CRS timeout for pci_device_is_present()

From: Vidya Sagar <vidyas@nvidia.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Sinan Kaya <okaya@kernel.org>,
	Thierry Reding <treding@nvidia.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	<jonathanh@nvidia.com>, <linux-tegra@vger.kernel.org>,
	<linux-pci@vger.kernel.org>, <kthota@nvidia.com>,
	<mmaddireddy@nvidia.com>, <sagar.tv@gmail.com>,
	"Andrew Murray" <andrew.murray@arm.com>,
	Lukas Wunner <lukas@wunner.de>
Subject: Re: [PATCH] PCI: Add CRS timeout for pci_device_is_present()
Date: Tue, 12 Nov 2019 23:29:41 +0530	[thread overview]
Message-ID: <453c4de8-b669-e76c-a2ad-bcdf50a47b57@nvidia.com> (raw)
In-Reply-To: <20191111223235.GA38578@google.com>

On 11/12/2019 4:02 AM, Bjorn Helgaas wrote:
> On Mon, Nov 11, 2019 at 11:31:18AM +0530, Vidya Sagar wrote:
>> On 11/6/2019 10:11 PM, Bjorn Helgaas wrote:
> 
>>> Based on Vidya's backtrace, I think the resume path with problems
>>> is this:
>>>
>>>     pci_pm_resume_noirq
>>>       pci_pm_default_resume_early
>>>         pci_power_up
>>>           if (platform_pci_power_manageable(dev))
>>>             platform_pci_set_power_state(dev, PCI_D0)  # <-- FW delay here?
>>>           pci_raw_set_power_state
>>>           pci_update_current_state
>>>             pci_device_is_present        # <-- config read returns CRS
>>>
>>> So I think your suggestion is that Vidya's firmware should be
>>> doing the delay inside platform_pci_set_power_state()?
>>>
>>> Vidya, you typically work on Tegra, so I assume this is on an
>>> arm64 system?  Does it have ACPI?  Do you have access to the
>>> firmware developers to ask about who they expect to do the delays?
>>
>> Yes. This is on arm64 (Tegra) and we don't have any ACPI or any
>> other firmware for that matter. PCIe is brought up directly in the
>> kernel.
> 
> I assume that your device is coming out of D3cold because apparently
> you're seeing a CRS status from the config read when
> pci_update_current_state() calls pci_device_is_present().  CRS status
> should only happen after reset or power-on from D3cold, and you're not
> doing a reset.
> 
> I'm pretty sure platform_pci_power_manageable() returns false on
> your system (can you confirm that?) because the only scenarios with
> platform power management are MID (Intel platform) and ACPI (which you
> don't have).
Yes. I can confirm that platform_pci_power_manageable() is false in case of
Tegra.

> 
> Maybe you have some other platform-specific mechanism that controls
> power to PCI devices, and it's not integrated into the
> platform_pci_*() framework?
> 
> Bjorn
>