linux-kernel - Re: [PATCH] Merge the Sonics Silicon Backplane subsystem

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Message-Id: <20070727123853.d16e875c.akpm@linux-foundation.org>
Date:	Fri, 27 Jul 2007 12:38:53 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michael Buesch <mb@...sch.de>
Cc:	"linux-kernel" <linux-kernel@...r.kernel.org>,
	bcm43xx-dev@...ts.berlios.de, netdev@...r.kernel.org,
	linux-wireless@...r.kernel.org,
	Gary Zambrano <zambrano@...adcom.com>
Subject: Re: [PATCH] Merge the Sonics Silicon Backplane subsystem

On Fri, 27 Jul 2007 21:30:48 +0200
Michael Buesch <mb@...sch.de> wrote:

> > ERROR: "foo * bar" should be "foo *bar"
> > #4156: FILE: drivers/ssb/ssb_private.h:119:
> > +extern struct ssb_bus * ssb_pci_dev_to_bus(struct pci_dev *pdev);
> > 
> > are worth addressing.
> 
> Well, I intentionally wrote that this way, as in my opinion
> it it easier to read. I only use this additional space for
> functions returning a pointer.
> 
> struct foo * function(int a, int b);
> 
> vs:
> 
> struct foo *function(int a, int b);
> 
> But I can change that, if that's really an issue and a
> style violation.

It's a microissue but yeah, no-space is more conventional.

> > > +static ssize_t ssb_pci_attr_sprom_show(struct device *pcidev,
> > > +				       struct device_attribute *attr,
> > > +				       char *buf)
> > > +{
> > > +	struct pci_dev *pdev = container_of(pcidev, struct pci_dev, dev);
> > > +	struct ssb_bus *bus;
> > > +	u16 *sprom;
> > > +	int err = -ENODEV;
> > > +	ssize_t count = 0;
> > > +
> > > +	bus = ssb_pci_dev_to_bus(pdev);
> > > +	if (!bus)
> > > +		goto out;
> > > +	err = -ENOMEM;
> > > +	sprom = kcalloc(SSB_SPROMSIZE_WORDS, sizeof(u16), GFP_KERNEL);
> > > +	if (!sprom)
> > > +		goto out;
> > > +
> > > +	err = -ERESTARTSYS;
> > > +	if (mutex_lock_interruptible(&bus->pci_sprom_mutex))
> > > +		goto out_kfree;
> > > +	sprom_do_read(bus, sprom);
> > > +	mutex_unlock(&bus->pci_sprom_mutex);
> > > +
> > > +	count = sprom2hex(sprom, buf, PAGE_SIZE);
> > > +	err = 0;
> > > +
> > > +out_kfree:
> > > +	kfree(sprom);
> > > +out:
> > > +	return err ? err : count;
> > > +}
> > 
> > The mutex_lock_interruptible() looks fishy.  Some commented explanation of
> > what it's doing would be good here.  It's quite unobvious to this reader. 
> > Cheesy deadlock avoidance?  Hope not.
> 
> No, it's simply to avoid writing the SPROM concurrently.
> SPROM writing is hairy and we must make sure here that
> we are the only one accessing the whole bus. We do that
> by suspending all devices and taking a lock to protect
> the SPROM from write concurrency.

Sure, but why is the locking interruptible rather than plain old
mutex_lock()?

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