linux-kernel - Re: [PATCH 1/1 linux-next] zd1201: replace kmalloc/memset by kzalloc

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Date:	Tue, 14 Oct 2014 20:08:34 +0200
From:	Bjørn Mork <bjorn@...k.no>
To:	Joe Perches <joe@...ches.com>
Cc:	Fabian Frederick <fabf@...net.be>, linux-kernel@...r.kernel.org,
	"John W. Linville" <linville@...driver.com>,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 1/1 linux-next] zd1201: replace kmalloc/memset by kzalloc

Joe Perches <joe@...ches.com> writes:

> And does this really need to be alloc'd?

Yes, it does. It is used as a transfer_buffer in usb_fill_bulk_urb() and
must be "suitable for DMA".  From include/linux/usb.h:

/**
 * struct urb - USB Request Block
..
 * @transfer_buffer:  This identifies the buffer to (or from) which the I/O
 *      request will be performed unless URB_NO_TRANSFER_DMA_MAP is set
 *      (however, do not leave garbage in transfer_buffer even then).
 *      This buffer must be suitable for DMA; allocate it with
 *      kmalloc() or equivalent.  For transfers to "in" endpoints, contents
 *      of this buffer will be modified.  This buffer is used for the data
 *      stage of control transfers.

Bjørn
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