From: Mauro Carvalho Chehab <mchehab@infradead.org>
To: wharms@bfs.de
Cc: Dan Carpenter <error27@gmail.com>,
Adams.xu@azwave.com.cn, linux-media@vger.kernel.org,
kernel-janitors@vger.kernel.org
Subject: Re: [patch -next 1/2] media/az6027: doing dma on the stack
Date: Thu, 06 May 2010 23:30:09 -0300 [thread overview]
Message-ID: <4BE37B31.5030907@infradead.org> (raw)
In-Reply-To: <4BE02F66.8060300@bfs.de>
walter harms wrote:
>
> Dan Carpenter schrieb:
>> I changed the dma buffers to use allocated memory instead of stack
>> memory.
>>
>> The reason for this is documented in Documentation/DMA-API-HOWTO.txt
>> under the section: "What memory is DMA'able?" That document was only
>> added a couple weeks ago and there are still lots of modules which
>> haven't been corrected yet. Btw. Smatch includes a pretty good test to
>> find places which use stack memory as a dma buffer. That's how I found
>> these. (http://smatch.sf.net).
>>
>> Signed-off-by: Dan Carpenter <error27@gmail.com>
>>
>> diff --git a/drivers/media/dvb/dvb-usb/az6027.c b/drivers/media/dvb/dvb-usb/az6027.c
>> index 8934788..baaa301 100644
>> --- a/drivers/media/dvb/dvb-usb/az6027.c
>> +++ b/drivers/media/dvb/dvb-usb/az6027.c
>> @@ -417,11 +417,15 @@ static int az6027_ci_read_attribute_mem(struct dvb_ca_en50221 *ca,
>> u16 value;
>> u16 index;
>> int blen;
>> - u8 b[12];
>> + u8 *b;
>>
>> if (slot != 0)
>> return -EINVAL;
>>
>> + b = kmalloc(12, GFP_KERNEL);
>> + if (!b)
>> + return -ENOMEM;
>> +
>> mutex_lock(&state->ca_mutex);
>>
>> req = 0xC1;
>
>
> Hi Dan,
> i am not sure if that is the way to go.
> iff i understand the code correctly the b[12] seems to overcommit only
> blen bytes (not 12) is needed. There must be a cheaper way to send a few bytes
> of space to send a command to a device. Perhaps gregKH has a hint ?
There is: you can add an array on a device private structure to hold
those memory transfers. For now, I'll add this patch, as it corrects
a real bug.
Cheers,
Mauro
prev parent reply other threads:[~2010-05-07 2:30 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-04 12:14 [patch -next 1/2] media/az6027: doing dma on the stack Dan Carpenter
2010-05-04 14:29 ` walter harms
2010-05-07 2:30 ` Mauro Carvalho Chehab [this message]
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