linux-kernel - Re: [PATCH v2 01/15] scsi: megaraid_sas: use generic power management

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Date:   Wed, 9 Sep 2020 08:23:32 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Vaibhav Gupta <vaibhavgupta40@...il.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Bjorn Helgaas <bjorn@...gaas.com>,
        Vaibhav Gupta <vaibhav.varodek@...il.com>,
        Adam Radford <aradford@...il.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Adaptec OEM Raid Solutions <aacraid@...rosemi.com>,
        Hannes Reinecke <hare@...e.com>,
        Bradley Grove <linuxdrivers@...otech.com>,
        John Garry <john.garry@...wei.com>,
        Don Brace <don.brace@...rosemi.com>,
        James Smart <james.smart@...adcom.com>,
        Dick Kennedy <dick.kennedy@...adcom.com>,
        Kashyap Desai <kashyap.desai@...adcom.com>,
        Sumit Saxena <sumit.saxena@...adcom.com>,
        Shivasharan S <shivasharan.srikanteshwara@...adcom.com>,
        Sathya Prakash <sathya.prakash@...adcom.com>,
        Sreekanth Reddy <sreekanth.reddy@...adcom.com>,
        Suganath Prabu Subramani 
        <suganath-prabu.subramani@...adcom.com>,
        Jack Wang <jinpu.wang@...ud.ionos.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-scsi@...r.kernel.org, esc.storagedev@...rosemi.com,
        megaraidlinux.pdl@...adcom.com, MPT-FusionLinux.pdl@...adcom.com
Subject: Re: [PATCH v2 01/15] scsi: megaraid_sas: use generic power management

On Wed, Sep 09, 2020 at 03:33:15PM +0530, Vaibhav Gupta wrote:
> On Tue, Sep 08, 2020 at 12:32:09PM -0500, Bjorn Helgaas wrote:
> > On Mon, Jul 20, 2020 at 07:04:14PM +0530, Vaibhav Gupta wrote:
> > > With legacy PM hooks, it was the responsibility of a driver to manage PCI
> > > states and also the device's power state. The generic approach is to let
> > > the PCI core handle the work.
> > > 
> > > PCI core passes "struct device*" as an argument to the .suspend() and
> > > .resume() callbacks. As the .suspend() work with "struct instance*",
> > > extract it from "struct device*" using dev_get_drv_data().
> > > 
> > > Driver was also using PCI helper functions like pci_save/restore_state(),
> > > pci_disable/enable_device(), pci_set_power_state() and pci_enable_wake().
> > > They should not be invoked by the driver.
> > > 
> > > Compile-tested only.
> > > 
> > > Signed-off-by: Vaibhav Gupta <vaibhavgupta40@...il.com>
> > > ---
> > >  drivers/scsi/megaraid/megaraid_sas_base.c | 61 ++++++-----------------
> > >  1 file changed, 16 insertions(+), 45 deletions(-)
> > > 
> > > diff --git a/drivers/scsi/megaraid/megaraid_sas_base.c b/drivers/scsi/megaraid/megaraid_sas_base.c
> > > index 00668335c2af..4a6ee7778977 100644
> > > --- a/drivers/scsi/megaraid/megaraid_sas_base.c
> > > +++ b/drivers/scsi/megaraid/megaraid_sas_base.c
> > > @@ -7539,25 +7539,21 @@ static void megasas_shutdown_controller(struct megasas_instance *instance,
> > >  	megasas_return_cmd(instance, cmd);
> > >  }
> > >  
> > > -#ifdef CONFIG_PM
> > >  /**
> > >   * megasas_suspend -	driver suspend entry point
> > > - * @pdev:		PCI device structure
> > > - * @state:		PCI power state to suspend routine
> > > + * @dev:		Device structure
> > >   */
> > > -static int
> > > -megasas_suspend(struct pci_dev *pdev, pm_message_t state)
> > > +static int __maybe_unused
> > > +megasas_suspend(struct device *dev)
> > >  {
> > > -	struct megasas_instance *instance;
> > > -
> > > -	instance = pci_get_drvdata(pdev);
> > > +	struct megasas_instance *instance = dev_get_drvdata(dev);
> > >  
> > >  	if (!instance)
> > >  		return 0;
> > >  
> > >  	instance->unload = 1;
> > >  
> > > -	dev_info(&pdev->dev, "%s is called\n", __func__);
> > > +	dev_info(dev, "%s is called\n", __func__);
> > >  
> > >  	/* Shutdown SR-IOV heartbeat timer */
> > >  	if (instance->requestorId && !instance->skip_heartbeat_timer_del)
> > > @@ -7579,7 +7575,7 @@ megasas_suspend(struct pci_dev *pdev, pm_message_t state)
> > >  
> > >  	tasklet_kill(&instance->isr_tasklet);
> > >  
> > > -	pci_set_drvdata(instance->pdev, instance);
> > > +	dev_set_drvdata(dev, instance);
> > 
> > It *might* be correct to replace "instance->pdev" with "dev", but it's
> > not obvious and deserves some explanation.  It's true that you can
> > replace &pdev->dev with dev, but I don't know anything about
> > instance->dev.

Sorry, I meant "instance->pdev" here.

> > I don't think this change is actually necessary, is it?
> > "instance->pdev" is still a pci_dev pointer, so pci_set_drvdata()
> > should work fine. ...
> > 
> There is no instance->dev . The 'dev' passed dev_set_drvdata() is
> same &pdev->dev. 

Yes, it's true that "dev" here is the same as the "&pdev->dev" we had
previously.  But we passed "instance->pdev" (not "pdev") to
pci_set_drvdata().  So the question is whether instance->pdev->dev ==
dev.

They *might* be the same, but I don't think it's obvious.

> The dev pointer used here, points to same value.
> 
> pci_get_drvdata() and pci_set_drvdata() invoke dev_get_drvdata() and
> dev_set_drvdata() respectively. And they do nothing else. Seems like
> additional unnecessary function calls and operations.