linux-kernel - Re: [PATCH v4] ARM: fix debug prints relevant to PCI devices

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Message-ID: <20140923150407.GJ5982@ulmo>
Date:	Tue, 23 Sep 2014 17:04:08 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Vidya Sagar <sagar.tv@...il.com>,
	Yijing Wang <wangyijing@...wei.com>,
	Jason Cooper <jason@...edaemon.net>,
	Will Deacon <will.deacon@....com>,
	Stephen Warren <swarren@...dia.com>,
	Krishna Thota <kthota@...dia.com>,
	linux-arm <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] ARM: fix debug prints relevant to PCI devices

On Tue, Sep 23, 2014 at 03:06:35PM +0100, Russell King - ARM Linux wrote:
> On Tue, Sep 23, 2014 at 07:56:01AM -0600, Bjorn Helgaas wrote:
> > This doesn't require any coordination with the PCI core, so I was just
> > leaving this up to the arch.  But I guess I can at least give you my
> > opinion :)
> 
> However, PCI core people have more knowledge of the issues here than I do.
> 
> > > diff --git a/arch/arm/kernel/bios32.c b/arch/arm/kernel/bios32.c
> > > index 17a26c1..03c56ba 100644
> > > --- a/arch/arm/kernel/bios32.c
> > > +++ b/arch/arm/kernel/bios32.c
> > > @@ -290,6 +290,7 @@ void pcibios_fixup_bus(struct pci_bus *bus)
> > >  {
> > >         struct pci_dev *dev;
> > >         u16 features = PCI_COMMAND_SERR | PCI_COMMAND_PARITY | PCI_COMMAND_FAST_BACK;
> > > +       bool has_pcie_dev = false;
> > >
> > >         /*
> > >          * Walk the devices on this bus, working out what we can
> > > @@ -298,6 +299,8 @@ void pcibios_fixup_bus(struct pci_bus *bus)
> > >         list_for_each_entry(dev, &bus->devices, bus_list) {
> > >                 u16 status;
> > >
> > > +               if (!has_pcie_dev)
> > > +                       has_pcie_dev = pci_is_pcie(dev);
> > >                 pci_read_config_word(dev, PCI_STATUS, &status);
> > >
> > >                 /*
> > > @@ -354,9 +357,11 @@ void pcibios_fixup_bus(struct pci_bus *bus)
> > >
> > >         /*
> > >          * Report what we did for this bus
> > > +        * (only if the bus doesn't have any PCIe devices)
> > >          */
> > > -       printk(KERN_INFO "PCI: bus%d: Fast back to back transfers %sabled\n",
> > > -               bus->number, (features & PCI_COMMAND_FAST_BACK) ? "en" : "dis");
> > > +       if (!has_pcie_dev)
> > > +               pr_info("PCI: bus%d: Fast back to back transfers %sabled\n",
> > > +                       bus->number, (features & PCI_COMMAND_FAST_BACK) ? "en" : "dis");
> > 
> > My first choice would be to just drop the printk altogether.
> 
> It can be useful information.
> 
> > If we want to keep the printk, it should be enough to test "bus->self
> > && !pci_is_pcie(bus->self)" to see whether Fast Back-to-Back can be
> > enabled.
> 
> This is exactly the kind of issue that needs to be picked up by core
> PCI people.

I agree. Wouldn't it be more useful to move this into the core?
Disabling fast back-to-back transfers hardly seems like an ARM-
specific "fixup" to me.

Thierry

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