Hi Hardik,
According to earlier mail from Sergio, I could be noticed that it is
totally ok to restrict number of buffers by driver. As matter of fact,
I was always considering about the H/W restriction and could find the
answer from his mail.
By the way, thank you for your answer.
Cheers,
Nate
On Tue, May 19, 2009 at 2:28 PM, Shah, Hardik <hardik.s...@ti.com> wrote:
> Hi Nate,
>
>
>> -----Original Message-----
>> From: Aguirre Rodriguez, Sergio Alberto
>> Sent: Tuesday, May 19, 2009 10:52 AM
>> To: Dongsoo, Nathaniel Kim; 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
>>
>> 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?
> [Shah, Hardik] Rotation requires the VRFB contexts and limited number of
> contexts are available. So maximum number of buffers is fixed to 4 when
> rotation is enabled.
>
> Thanks,
> Hardik
>> >
>> >
>> >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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