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. -- Regards, Laurent Pinchart -- 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
