linux-kernel - Re: [PATCH v2] vgaarb: Use dev

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Message-ID: <20161117202059.GA22428@bhelgaas-glaptop.roam.corp.google.com>
Date:   Thu, 17 Nov 2016 14:20:59 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Bjorn Helgaas <bhelgaas@...gle.com>,
        David Airlie <airlied@...ux.ie>,
        Thierry Reding <treding@...dia.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2] vgaarb: Use dev_printk() when possible

On Thu, Nov 17, 2016 at 07:59:21PM +0100, Daniel Vetter wrote:
> On Thu, Nov 17, 2016 at 11:47:58AM -0600, Bjorn Helgaas wrote:
> > Use dev_printk() when possible.  This makes messages more consistent with
> > other device-related messages and, in some cases, adds useful information.
> > This changes messages like this:
> > 
> >   vgaarb: failed to allocate pci device
> >   vgaarb: setting as boot device: PCI:0000:01:00.0
> >   vgaarb: device added: PCI:0000:01:00.0,decodes=io+mem,owns=io+mem,locks=none
> >   vgaarb: bridge control possible 0000:01:00.0
> > 
> > to this:
> > 
> >   pci 0000:01:00.0: vgaarb: failed to allocate VGA arbiter data
> >   pci 0000:01:00.0: vgaarb: setting as boot VGA device
> >   pci 0000:01:00.0: vgaarb: VGA device added: decodes=io+mem,owns=io+mem,locks=none
> >   pci 0000:01:00.0: vgaarb: bridge control possible
> > 
> > No functional change intended.
> 
> Found one more nit below where there was one relevant change that
> shouldn't be here.

> > @@ -1189,24 +1194,25 @@ static ssize_t vga_arb_write(struct file *file, const char __user *buf,
> >  				ret_val = -EPROTO;
> >  				goto done;
> >  			}
> > -			pr_debug("%s ==> %x:%x:%x.%x\n", curr_pos,
> > -				domain, bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
> > -
> >  			pdev = pci_get_domain_bus_and_slot(domain, bus, devfn);
> > -			pr_debug("pdev %p\n", pdev);
> >  			if (!pdev) {
> > -				pr_err("invalid PCI address %x:%x:%x\n",
> > -					domain, bus, devfn);
> > +				pr_err("invalid PCI address %04x:%02x:%02x.%x\n",
> > +					domain, bus, PCI_SLOT(devfn),
> > +					PCI_FUNC(devfn));
> 
> Userspace-triggerable dmesg spam is imo not good, this needs to stay at
> debug level.

I did move these around slightly, but I don't *think* I changed
anything from debug to err level.  Previously:

  pr_debug("%s ==> %x:%x:%x.%x\n", ...);
  pdev = pci_get_domain_bus_and_slot(...);
  pr_debug("pdev %p\n", pdev);
  if (!pdev) {
    pr_err("invalid PCI address %x:%x:%x\n", ...);
  }

after my patch:

  pdev = pci_get_domain_bus_and_slot(...);
  if (!pdev) {
    pr_err("invalid PCI address %x:%x:%x\n", ...);
  }
  pr_debug("%s ==> %x:%x:%x.%x pdev %p\n", ...);

The pr_err() was there before.  I'd be glad to change that to a
pr_debug() if you prefer.

Bjorn