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Date:	Thu, 20 Dec 2012 14:18:49 +0530
From:	Venu Byravarasu <>
To:	Stephen Warren <>
CC:	"" <>,
	"" <>,
	"" <>,
	"" <>
Subject: RE: [PATCH] usb: phy: tegra: Using devm API for memory allocation

> -----Original Message-----
> From: Stephen Warren []
> Sent: Wednesday, December 19, 2012 11:08 PM
> To: Venu Byravarasu
> Cc:;; linux-
> Subject: Re: [PATCH] usb: phy: tegra: Using devm API for memory allocation
> On 12/18/2012 10:38 PM, Venu Byravarasu wrote:
> >> -----Original Message-----
> >> From: Stephen Warren []
> >> Sent: Tuesday, December 18, 2012 10:03 PM
> >> To: Venu Byravarasu
> >> Cc:;; linux-
> >>;
> >> Subject: Re: [PATCH] usb: phy: tegra: Using devm API for memory
> allocation
> >>
> >
> > Stephen,
> > As you mentioned I can replace kmalloc with kzalloc in the original code
> > and push an updated patch.
> > However, I just wanted to understand if there exists any issue
> > in using devm_kzalloc instead of kzalloc?
> devm_* are intended for objects allocated during probe(), and free()d
> during remove(). The object you're allocating here isn't that case.
> Now, once you convert the Tegra PHY driver to be a true device, perhaps
> this object will be allocated/freed during probe/remove, so the devm_
> functions will be useful then?
> The problem this may cause is a memory leak. Consider the Tegra EHCI and
> PHY drivers being built as modules, the PHY driver module being inserted
> and never removed, yet the EHCI driver being continually inserted and
> removed. Since the PHY is never removed, the memory allocated by its
> devm_kzalloc() call is never freed, but it's continually re-allocated
> since tegra_usb_phy_open() is called whenever the EHCI driver module is
> inserted. You need the explicit kfree() to avoid that, and since you're
> kfree()ing somewhere other than remove(), using devm_* to make the
> allocation isn't appropriate.
Thanks Stephen for the detailed explanation.
Sent updated patch for review: .

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