linux-kernel - RE: [PATCH] Video/UVC: Port mainlined uvc video driver to NOMMU

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Date:	Mon, 10 Nov 2008 11:30:19 -0000
From:	"Hennerich, Michael" <Michael.Hennerich@...log.com>
To:	"Laurent Pinchart" <laurent.pinchart@...net.be>,
	"Bryan Wu" <cooloney@...nel.org>
Cc:	<linux-uvc-devel@...ts.berlios.de>, <video4linux-list@...hat.com>,
	<linux-kernel@...r.kernel.org>,
	"Michael Hennerich" <michael.hennerich@...log.com>
Subject: RE: [PATCH] Video/UVC: Port mainlined uvc video driver to NOMMU



>-----Original Message-----
>From: Laurent Pinchart [mailto:laurent.pinchart@...net.be]
>Sent: Sunday, November 09, 2008 10:22 PM
>To: Bryan Wu
>Cc: linux-uvc-devel@...ts.berlios.de; video4linux-list@...hat.com;
linux-
>kernel@...r.kernel.org; Michael Hennerich
>Subject: Re: [PATCH] Video/UVC: Port mainlined uvc video driver to
NOMMU
>
>Hi Bryan, Michael,
>
>On Thursday 06 November 2008, Bryan Wu wrote:
>> From: Michael Hennerich <michael.hennerich@...log.com>
>>
>> Add NOMMU mmap support.
>>
>> Signed-off-by: Michael Hennerich <michael.hennerich@...log.com>
>> Signed-off-by: Bryan Wu <cooloney@...nel.org>
>> ---
>>  drivers/media/video/uvc/uvc_v4l2.c |   14 ++++++++++++++
>>  1 files changed, 14 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/media/video/uvc/uvc_v4l2.c
>> b/drivers/media/video/uvc/uvc_v4l2.c index 758dfef..2237f5e 100644
>> --- a/drivers/media/video/uvc/uvc_v4l2.c
>> +++ b/drivers/media/video/uvc/uvc_v4l2.c
>> @@ -1050,6 +1050,7 @@ static int uvc_v4l2_mmap(struct file *file,
struct
>> vm_area_struct *vma) break;
>>  	}
>>
>> +#ifdef CONFIG_MMU
>>  	if (i == video->queue.count || size != video->queue.buf_size) {
>>  		ret = -EINVAL;
>>  		goto done;
>> @@ -1071,7 +1072,20 @@ static int uvc_v4l2_mmap(struct file *file,
struct
>> vm_area_struct *vma) addr += PAGE_SIZE;
>>  		size -= PAGE_SIZE;
>>  	}
>> +#else
>> +	if (i == video->queue.count ||
>> +		PAGE_ALIGN(size) != video->queue.buf_size) {
>
>Just out of curiosity, why do you need to PAGE_ALIGN size for non-MMU
>platforms ?

Size and video->queue.buf_size is not the 100% same size (off by a few
bytes < pagesize), I think it's because on NOMMU the kernel calls
kmalloc() to allocate the buffer, not get_free_page().


>
>> +		ret = -EINVAL;
>> +		goto done;
>> +	}
>> +
>> +	vma->vm_flags |= VM_IO | VM_MAYSHARE; /*
documentation/nommu-mmap.txt
>*/
>
>VM_MAYSHARE is not documented anywhere in Documentation/ in Linux
2.6.28-
>rc3.
>Why is it needed for non-MMU architectures only ?

mmap on NOMMU is a bit tricky and very restricted.
In case user does a MAP_SHARED with some combination of the PROT_###
Flags the mmap fails. What's allowed and what's not is documented in
documentation/nommu-mmap.txt
Setting VM_MAYSHARE allows user MAP_PRIVATE mappings.
 
-Michael

>
>> +
>> +	addr = (unsigned long)video->queue.mem + buffer->buf.m.offset;
>>
>> +	vma->vm_start = addr;
>> +	vma->vm_end = addr +  video->queue.buf_size;
>> +#endif
>>  	vma->vm_ops = &uvc_vm_ops;
>>  	vma->vm_private_data = buffer;
>>  	uvc_vm_open(vma);
>
>Best regards,
>
>Laurent Pinchart
--
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