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Subject: Re: [PATCH] PCI: Add CRS timeout for pci_device_is_present()
To:     Bjorn Helgaas <helgaas@kernel.org>
CC:     Thierry Reding <treding@nvidia.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
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        Lukas Wunner <lukas@wunner.de>
References: <20191115223647.GA129381@google.com>
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From:   Vidya Sagar <vidyas@nvidia.com>
Message-ID: <31b03468-c2ee-4347-51ab-6a15a23cda01@nvidia.com>
Date:   Mon, 18 Nov 2019 20:48:12 +0530
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On 11/16/2019 4:06 AM, Bjorn Helgaas wrote:
> On Fri, Nov 15, 2019 at 03:34:23PM +0530, Vidya Sagar wrote:
>> On 11/15/2019 12:06 AM, Bjorn Helgaas wrote:
>>> On Wed, Nov 13, 2019 at 12:20:43PM +0100, Thierry Reding wrote:
>>>> On Tue, Nov 12, 2019 at 12:58:44PM -0600, Bjorn Helgaas wrote:
>>>>
>>>>> My question is whether this wait should be connected somehow with
>>>>> platform_pci_set_power_state().  It sounds like the tegra host
>>>>> controller driver already does the platform-specific delays, and I'm
>>>>> not sure it's reasonable for platform_pci_set_power_state() to do the
>>>>> CRS polling.  Maybe something like this?  I'd really like to get
>>>>> Rafael's thinking here.
>>>>>
>>>>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>>>>> index e7982af9a5d8..052fa316c917 100644
>>>>> --- a/drivers/pci/pci.c
>>>>> +++ b/drivers/pci/pci.c
>>>>> @@ -964,9 +964,14 @@ void pci_refresh_power_state(struct pci_dev *dev)
>>>>>     */
>>>>>    void pci_power_up(struct pci_dev *dev)
>>>>>    {
>>>>> +	pci_power_state_t prev_state = dev->current_state;
>>>>> +
>>>>>    	if (platform_pci_power_manageable(dev))
>>>>>    		platform_pci_set_power_state(dev, PCI_D0);
>>>>> +	if (prev_state == PCI_D3cold)
>>>>> +		pci_dev_wait(dev, "D3cold->D0", PCIE_RESET_READY_POLL_MS);
>>
>> Is there any specific reason why should there be a check for the
>> state?  In Tegra series, I observe that, by the time execution comes
>> to this point, prev_state is PCI_D3Hot and in Tegra194 particularly,
>> it is PCI_D0 because the host controller driver explicitly keeps the
>> downstream devices in PCI_D0 state as a work around for one of the
>> Tegra194 specific issues.
> 
> I think you're right, we probably should not try to check "prev_state"
> here because we can't rely on that being accurate.
> 
> On Tegra, I assume suspend puts the PCIe devices in D3hot, then when
> we suspend the RC itself, it looks like tegra_pcie_pm_suspend()
> actually turns off the power, so the PCIe devices probably go to
> D3cold but nothing updates their dev->current_state, so it's probably
> still PCI_D3hot.
> 
> On Tegra194, the same probably happens, except that when we suspend
> the RC itself, tegra_pcie_downstream_dev_to_D0() puts the PCIe devices
> back in D0 (updating their dev->current_state to PCI_D0), and then we
> turn off the power, so they probably also end up in D3cold but with
> dev_current_state still set to PCI_D0.
> 
>> So, I feel the check for current_state may not be need here(?)
> 
> I think you're right.  We can't tell what dev->current_state is when
> we enter pci_power_up().
Thanks,
I'll push a change with your suggested modifications.

- Vidya Sagar
> 
> Bjorn
>