Hi Sergio,
Thank you for your explanation . I learned much from that.
Cheers,
Nate
On Tue, May 19, 2009 at 2:22 PM, Aguirre Rodriguez, Sergio Alberto
<saagui...@ti.com> wrote:
> Hi Nate,
>
> I have 1 input regarding your question:
>
>>From: linux-media-ow...@vger.kernel.org [linux-media-ow...@vger.kernel.org]
>>On Behalf Of Dongsoo, Nathaniel Kim [dongsoo....@gmail.com]
>>Sent: Tuesday, May 19, 2009 7:53 AM
>>To: Shah, Hardik
>>Cc: linux-me...@vger.kernel.org; linux-omap@vger.kernel.org; Jadav, Brijesh
>>R; Hiremath, Vaibhav
>>Subject: Re: [PATCH 3/3] OMAP2/3 V4L2 Display Driver
>>
>>Hello Hardik,
>>
>>Reviewing your driver, I found something made me curious.
>>
>>
>>On Wed, Apr 22, 2009 at 3:25 PM, Hardik Shah <hardik.s...@ti.com> wrote:
>
> <snip>
>
>>> +/* Buffer setup function is called by videobuf layer when REQBUF ioctl is
>>> + * called. This is used to setup buffers and return size and count of
>>> + * buffers allocated. After the call to this buffer, videobuf layer will
>>> + * setup buffer queue depending on the size and count of buffers
>>> + */
>>> +static int omap_vout_buffer_setup(struct videobuf_queue *q, unsigned int
>>> *count,
>>> + unsigned int *size)
>>> +{
>>> + struct omap_vout_device *vout = q->priv_data;
>>> + int startindex = 0, i, j;
>>> + u32 phy_addr = 0, virt_addr = 0;
>>> +
>>> + if (!vout)
>>> + return -EINVAL;
>>> +
>>> + if (V4L2_BUF_TYPE_VIDEO_OUTPUT != q->type)
>>> + return -EINVAL;
>>> +
>>> + startindex = (vout->vid == OMAP_VIDEO1) ?
>>> + video1_numbuffers : video2_numbuffers;
>>> + if (V4L2_MEMORY_MMAP == vout->memory && *count < startindex)
>>> + *count = startindex;
>>> +
>>> + if ((rotation_enabled(vout->rotation)) && *count > 4)
>>> + *count = 4;
>>> +
>>
>>
>>
>>This seems to be weird to me. If user requests multiple buffers more
>>than 4, user cannot recognize that the number of buffers requested is
>>forced to change into 4. I'm not sure whether this could be serious or
>>not, but it is obvious that user can have doubt about why if user have
>>no information about the OMAP H/W.
>>Is it really necessary to be configured to 4?
>>
>>
>>Cheers,
>>
>>Nate
>>
>
> We did a very similar thing on omap3 camera driver, not exactly by the number
> of buffers requested, but more about checking if the bytesize of the total
> requested buffers was superior to the MMU fixed sized page table size
> capabilities to map that size, then we were limiting the number of buffers
> accordingly (for keeping the page table size fixed).
>
> According to the v4l2 spec, changing the count value should be valid, and it
> is the userspace app responsability to check the value again, to confirm how
> many of the requested buffers are actually available.
>
> Regards,
> Sergio
--
=
DongSoo, Nathaniel Kim
Engineer
Mobile S/W Platform Lab.
Digital Media & Communications R&D Centre
Samsung Electronics CO., LTD.
e-mail : dongsoo....@gmail.com
dongsoo45....@samsung.com
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