linux-kernel - Re: [PATCH] drivers: rtl818x: request DMA-able memory

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Date:	Mon, 25 Oct 2010 15:11:22 +0100
From:	Hin-Tak Leung <htl10@...rs.sourceforge.net>
To:	Larry Finger <Larry.Finger@...inger.net>
CC:	Serafeim Zanikolas <sez@...ian.org>, herton@...driva.com.br,
	linville@...driver.com, joe@...ches.com, davem@...emloft.net,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers: rtl818x: request DMA-able memory



Larry Finger wrote:
> On 10/24/2010 03:32 PM, Serafeim Zanikolas wrote:
>> Despite the indicated intention in comment, the kmalloc() call was not
>> explicitly requesting memory from ZONE_DMA.
>>
>> Signed-off-by: Serafeim Zanikolas <sez@...ian.org>
>> ---
>>  drivers/net/wireless/rtl818x/rtl8187_dev.c |    3 ++-
>>  1 files changed, 2 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/net/wireless/rtl818x/rtl8187_dev.c b/drivers/net/wireless/rtl818x/rtl8187_dev.c
>> index 38fa824..771794d 100644
>> --- a/drivers/net/wireless/rtl818x/rtl8187_dev.c
>> +++ b/drivers/net/wireless/rtl818x/rtl8187_dev.c
>> @@ -1343,7 +1343,8 @@ static int __devinit rtl8187_probe(struct usb_interface *intf,
>>  	priv->is_rtl8187b = (id->driver_info == DEVICE_RTL8187B);
>>  
>>  	/* allocate "DMA aware" buffer for register accesses */
>> -	priv->io_dmabuf = kmalloc(sizeof(*priv->io_dmabuf), GFP_KERNEL);
>> +	priv->io_dmabuf = kmalloc(sizeof(*priv->io_dmabuf),
>> +				  GFP_DMA | GFP_KERNEL);
>>  	if (!priv->io_dmabuf) {
>>  		err = -ENOMEM;
>>  		goto err_free_dev;
> 
> ACK.
> 
> Larry

Acked-by: Hin-Tak Leung <htl10@...rs.sourceforge.net>

I had a quick look for similiar constructs and AFAIK only the b43/b43legacy 
drivers uses DMA buffers. Seems to be a rare practice. Is that something we 
should or should not do?

Hin-Tak
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