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From: Dan Williams <dan.j.williams@intel.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: "Kuppuswamy,
	Sathyanarayanan"  <sathyanarayanan.kuppuswamy@linux.intel.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Linux PCI <linux-pci@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	Keith Busch <keith.busch@intel.com>,
	knsathya@kernel.org, Lukas Wunner <lukas@wunner.de>
Subject: Re: [PATCH v1 1/1] PCI: pciehp: Skip DLLSC handling if DPC is triggered
Date: Fri, 12 Mar 2021 16:37:49 -0800	[thread overview]
Message-ID: <CAPcyv4jWkwbaBUtcV4B1hMaCWxEdZwzgmLSTiuepb-MQE=ZegA@mail.gmail.com> (raw)
In-Reply-To: <20210312231416.GA2304029@bjorn-Precision-5520>

On Fri, Mar 12, 2021 at 3:14 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Fri, Mar 12, 2021 at 02:11:03PM -0800, Kuppuswamy, Sathyanarayanan wrote:
> > On 3/12/21 1:33 PM, Bjorn Helgaas wrote:
> > > On Mon, Mar 08, 2021 at 10:34:10PM -0800, sathyanarayanan.kuppuswamy@linux.intel.com wrote:
> > > > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>
> > > > +bool is_dpc_reset_active(struct pci_dev *dev)
> > > > +{
> > > > + struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
> > > > + u16 status;
> > > > +
> > > > + if (!dev->dpc_cap)
> > > > +         return false;
> > > > +
> > > > + /*
> > > > +  * If DPC is owned by firmware and EDR is not supported, there is
> > > > +  * no race between hotplug and DPC recovery handler. So return
> > > > +  * false.
> > > > +  */
> > > > + if (!host->native_dpc && !IS_ENABLED(CONFIG_PCIE_EDR))
> > > > +         return false;
> > > > +
> > > > + if (atomic_read_acquire(&dev->dpc_reset_active))
> > > > +         return true;
> > > > +
> > > > + pci_read_config_word(dev, dev->dpc_cap + PCI_EXP_DPC_STATUS, &status);
> > > > +
> > > > + return !!(status & PCI_EXP_DPC_STATUS_TRIGGER);
> > >
> > > I know it's somewhat common in drivers/pci/, but I'm not really a
> > > big fan of "!!".
> > I can change it to use ternary operator.
> > (status & PCI_EXP_DPC_STATUS_TRIGGER) ? true : false;
>
> Ternary isn't terrible, but what's wrong with:
>
>   if (status & PCI_EXP_DPC_STATUS_TRIGGER)
>     return true;
>   return false;

It was the branch I was trying to get rid of by recommending !!, how about:

return (status & PCI_EXP_DPC_STATUS_TRIGGER) == PCI_EXP_DPC_STATUS_TRIGGER;

...just so I know the style preference for future drivers/pci/ work?
That at least matches the pattern in the mm helpers that test pte
bits.

>
> which matches the style of the rest of the function.
>
> Looking at this again, we return "true" if either dpc_reset_active or
> PCI_EXP_DPC_STATUS_TRIGGER.  I haven't worked this all out, but that
> pattern feels racy.  I guess the thought is that if
> PCI_EXP_DPC_STATUS_TRIGGER is set, dpc_reset_link() will be invoked
> soon and we don't want to interfere?

Right, and when the trigger is clear then dpc_reset_active keeps
holding off the hotplug driver until the dpc reset completes in
polling for the link up event.

      parent reply	other threads:[~2021-03-13  0:39 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-09  6:34 [PATCH v1 1/1] PCI: pciehp: Skip DLLSC handling if DPC is triggered sathyanarayanan.kuppuswamy
2021-03-12 21:33 ` Bjorn Helgaas
2021-03-12 22:11   ` Kuppuswamy, Sathyanarayanan
2021-03-12 23:14     ` Bjorn Helgaas
2021-03-12 23:26       ` Kuppuswamy, Sathyanarayanan
2021-03-13  0:37       ` Dan Williams [this message]

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