On 11/11/2016 02:57 PM, Laurent Pinchart wrote: > Hi Hans, > > On Friday 11 Nov 2016 14:53:58 Hans Verkuil wrote: >> On 11/10/2016 09:08 AM, Laurent Pinchart wrote: >>> Antti, Hans, ping ? Please see below. >>> >>> On Friday 04 Nov 2016 09:23:29 Ramesh Shanmugasundaram wrote: >>>>> On 11/02/2016 10:58 PM, Laurent Pinchart wrote: >>>>>> On Wednesday 02 Nov 2016 09:00:00 Ramesh Shanmugasundaram wrote: >>>>>>>>> On Wednesday 12 Oct 2016 15:10:29 Ramesh Shanmugasundaram wrote: >>>>>>>>>> This patch adds documentation for the three new SDR formats >>>>>>>>>> >>>>>>>>>> V4L2_SDR_FMT_SCU16BE >>>>>>>>>> V4L2_SDR_FMT_SCU18BE >>>>>>>>>> V4L2_SDR_FMT_SCU20BE >>>>>>> >>>>>>> [snip] >>>>>>> >>>>>>>>>> + >>>>>>>>>> + - start + 0: >>>>>>>>>> + >>>>>>>>>> + - I'\ :sub:`0[D13:D6]` >>>>>>>>>> + >>>>>>>>>> + - I'\ :sub:`0[D5:D0]` >>>>>>>>>> + >>>>>>>>>> + - .. row 2 >>>>>>>>>> + >>>>>>>>>> + - start + buffer_size/2: >>>>>>>>>> + >>>>>>>>>> + - Q'\ :sub:`0[D13:D6]` >>>>>>>>>> + >>>>>>>>>> + - Q'\ :sub:`0[D5:D0]` >>>>>>>>> >>>>>>>>> The format looks planar, does it use one V4L2 plane (as does NV12) >>>>>>>>> or two V4L2 planes (as does NV12M) ? Same question for the other >>>>>>>>> formats. >>>>>>>> >>>>>>>> Thank you for bringing up this topic. This is one of the key design >>>>>>>> dilemma. >>>>>>>> >>>>>>>> The I & Q data for these three SDR formats comes from two different >>>>>>>> DMA channels and hence two separate pointers -> we could say it is >>>>>>>> v4l2 multi- planar. Right now, I am making it look like a single >>>>>>>> plane by presenting the data in one single buffer ptr. >>>>>>>> >>>>>>>> For e.g. multi-planar SC16 format would look something like this >>>>>>>> >>>>>>>> <------------------------32bits----------------------> >>>>>>>> <--I(14 bit data) + 2bit status--16bit padded zeros--> : start0 + 0 >>>>>>>> <--I(14 bit data) + 2bit status--16bit padded zeros--> : start0 + 4 >>>>>>>> ... >>>>>>>> <--Q(14 bit data) + 2bit status--16bit padded zeros--> : start1 + 0 >>>>>>>> <--Q(14 bit data) + 2bit status--16bit padded zeros--> : start1 + 4 >>>>>>>> >>>>>>>> My concerns are >>>>>>>> >>>>>>>> 1) These formats are not a standard as the video "Image Formats". >>>>>>>> These formats are possible when we use DRIF + MAX2175 combination. >>>>>>>> If we interface with a different tuner vendor, the above format(s) >>>>>>>> MAY/MAY NOT be re-usable. We do not know at this point. This is the >>>>>>>> main open item for discussion in the cover letter. >>>>>> >>>>>> If the formats are really device-specific then they should be >>>>>> documented accordingly and not made generic. >>>>>> >>>>>>>> 2) MPLANE support within V4L2 seems specific to video. Please >>>>>>>> correct me if this is wrong interpretation. >>>>>>>> >>>>>>>> - struct v4l2_format contains v4l2_sdr_format and >>>>>>>> v4l2_pix_format_mplane as members of union. Should I create a new >>>>>>>> v4l2_sdr_format_mplane? If I have to use v4l2_pix_format_mplane most >>>>>>>> of the video specific members would be unused (it would be similar >>>>>>>> to using v4l2_pix_format itself instead of v4l2_sdr_format)? >>>>>> >>>>>> I have no answer to that question as I'm not familiar with SDR. Antti, >>>>>> you've added v4l2_sdr_format to the API, what's your opinion ? Hans, >>>>>> as you've acked the patch, your input would be appreciated as well. >>>>> >>>>> If I understood correctly this hardware provides I and Q samples via >>>>> different channels and driver now combines those channels as a >>>>> sequential >>>>> IQ sample pairs. >>>> >>>> The driver combines the two buffer ptrs and present as one single buffer. >>>> For a buffer of size 200 >>>> >>>> ptr + 0 : I I I I ... I >>>> ptr + 100 : Q Q Q Q ... Q >>>> >>>>> I have never seen any other than hw which provides IQ IQ IQ IQ ... IQ. >>>> >>>> There are some modes where this h/w combo can also do IQ IQ IQ pattern. >>>> Those modes are not added in the RFC patchset. >>>> >>>>> This is >>>>> I I I I ... I >>>>> Q Q Q Q ... Q >>>>> I am not very familiar with planars, but it sounds like it is correct >>>>> approach. So I think should be added rather than emulate packet >>>>> sequential format. >>>> >>>> My understanding of V4L2 MPLANE constructs is limited to a quick code >>>> read >>>> only. At this point MPLANE support seems specific to video. SDR is >>>> defined >>>> as separate format like v4l2_pix_format. Questions would be - should we >>>> define new SDR_MPLANE? or merge SDR format with pix format & reuse >>>> existing >>>> MPLANE with some SDR extensions (if possible)? These seem big design >>>> decisions. Any suggestions please? >>>> >>>> For my use case, MPLANE support does not seem to add significant benefit >>>> except it may be syntactically correct. I am doing cyclic DMA with a >>>> small >>>> set of h/w buffers and copying each stage to one mmapped vmalloc >>>> vb2_buffer >>>> at two offsets. If we add MPLANE support, it can be two non-contiguous >>>> buffer pointers. >>>> >>>>>>>> - The above decision (accomodate SDR & MPLANE) needs to be >>>>>>>> propagated across the framework. Is this the preferred approach? >>>>>>>> >>>>>>>> It goes back to point (1). As of today, the change set for this >>>>>>>> combo (DRIF+MAX2175) introduces new SDR formats only. Should it add >>>>>>>> further SDR+MPLANE support to the framework as well? >>>>>>>> >>>>>>>> I would appreciate your suggestions on this regard. >> >> Some terminology first: >> >> Planar formats separate the data into different memory areas: in this case >> one part is all I and one part is all Q. This as opposed to interleaved >> formats (IQIQIQIQ....). >> >> As long as both planes fit in the same buffer all is fine. Since that is >> the case here there is no need to introduce a new MPLANE API. >> >> The MPLANE API was added for video to handle cases where the two planes >> had to be in two different non-contiguous buffers. > > Not only that, it can also be used for cases where storing the two planes in > separate buffers can be beneficial, even if a single contiguous buffer could > work. > >> So instead of passing one buffer pointer, you need to pass two or more >> buffer pointers. >> >> In hindsight we should have called it the MBUFFER API. > > The name was badly chosen, yes. > >> Oh well... >> >> Anyway, since there is no problem here apparently to keep both planes >> in one buffer there is also no need to introduce a SDR_MPLANE. > > The question here is whether there could be a benefit in separating I and Q > data in two buffers compared to storing them in the same buffer. > The MPLANE API is very messy and introducing something like SDR_MPLANE is not something I would promote. If we want that, then we should first make a new v4l2_buffer struct that simplifies MPLANE handling (we discussed that before). Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
