linux-kernel - Re: [PATCH] usb: core: config.c: usb_get

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Message-ID: <Pine.LNX.4.44L0.1004171212550.6609-100000@netrider.rowland.org>
Date:	Sat, 17 Apr 2010 12:13:34 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Michal Nazarewicz <mina86@...a86.com>
cc:	linux-usb@...r.kernel.org, <Linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH] usb: core: config.c: usb_get_configuration() simplified

On Sat, 17 Apr 2010, Michal Nazarewicz wrote:

> usb_gat_configuratio() used two pointers to point to the same
> memory.  Code simplified, by removing one of them.
> 
> Signed-off-by: Michal Nazarewicz <mina86@...a86.com>
> ---
>  drivers/usb/core/config.c |   10 ++++------
>  1 files changed, 4 insertions(+), 6 deletions(-)
> 
> > On Sat, 17 Apr 2010, Michal Nazarewicz wrote:
> >> usb_get_configuration() uses a temporary buffer allocated on heap
> >> to read USB configuration descriptor.  The buffer is just nine
> >> bytes an so it is a waste to allocate it on heap where it can be
> >> allocated on stack with the rest of local variables.  This
> >> simplifies the code and minimises memory usage.
> 
> Alan Stern <stern@...land.harvard.edu> writes:
> > This is completely wrong.  You are not allowed to do DMA to buffers on 
> > the stack; some architectures are not capable of handling it.
> 
> That makes sense; I haven't considered this thinking that copying nine
> bytes by CPU, rather then using DMA, is not a big issue.
> 
> Still, the change proposed by attached commit does not suffer from DMA
> issue and still simplify the code.

Yes, this is fine.

Alan Stern

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