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Subject: Re: [PATCH v1] i2c: nvidia-gpu: drop empty stub for runtime pm
To:     Vaibhav Gupta <vaibhavgupta40@gmail.com>,
        Ajay Gupta <ajayg@nvidia.com>
Cc:     Bjorn Helgaas <helgaas@kernel.org>, linux-i2c@vger.kernel.org,
        linux-kernel@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>
References: <20201107082151.58239-1-vaibhavgupta40@gmail.com>
 <20201107090442.GA107675@gmail.com>
From:   Jarkko Nikula <jarkko.nikula@linux.intel.com>
Message-ID: <6989eb51-a36c-6e43-86f3-9b02ab490d95@linux.intel.com>
Date:   Tue, 10 Nov 2020 14:33:43 +0200
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On 11/7/20 11:04 AM, Vaibhav Gupta wrote:
> On Sat, Nov 07, 2020 at 01:51:51PM +0530, Vaibhav Gupta wrote:
>> After the commit c5eb1190074c ("PCI / PM: Allow runtime PM without callback
>> functions") we no more need empty stubs for runtime-pm to work.
>>
>> The driver has no device specific task(s) for .suspend() . The stub was
>> placed just for runtime-pm, which can be dropped now.
>>
>> Reported-by: Bjorn Helgaas <bhelgaas@google.com>
>> Signed-off-by: Vaibhav Gupta <vaibhavgupta40@gmail.com>
>> ---
>>   drivers/i2c/busses/i2c-nvidia-gpu.c | 10 +---------
>>   1 file changed, 1 insertion(+), 9 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-nvidia-gpu.c b/drivers/i2c/busses/i2c-nvidia-gpu.c
>> index f9a69b109e5c..6b20601ffb13 100644
>> --- a/drivers/i2c/busses/i2c-nvidia-gpu.c
>> +++ b/drivers/i2c/busses/i2c-nvidia-gpu.c
>> @@ -353,15 +353,7 @@ static void gpu_i2c_remove(struct pci_dev *pdev)
>>   	pci_free_irq_vectors(pdev);
>>   }
>>   
>> -/*
>> - * We need gpu_i2c_suspend() even if it is stub, for runtime pm to work
>> - * correctly. Without it, lspci shows runtime pm status as "D0" for the card.
>> - * Documentation/power/pci.rst also insists for driver to provide this.
>> - */
>> -static __maybe_unused int gpu_i2c_suspend(struct device *dev)
>> -{
>> -	return 0;
>> -}
>> +#define gpu_i2c_suspend NULL
>>   
Perhaps we can put NULL directly into UNIVERSAL_DEV_PM_OPS() for the 
suspend callback?

>>   static __maybe_unused int gpu_i2c_resume(struct device *dev)
>>   {
>> -- 
>> 2.28.0
>>
> The patch is only compile-tested.
> 
It should work also system suspend point of view. This patch affects 
also it since callbacks are set with the UNIVERSAL_DEV_PM_OPS(). Means 
the same callback is used for runtime PM and system suspend.

I quickly debugged this with an another driver and PCI stack does put 
the device into D3 state in system suspend from pci_prepare_to_sleep() 
if the suspend callback is not set and device was on prior it.

Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>