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Subject: Re: [PATCH v6 4/6] media: i2c: Add TDA1997x HDMI receiver driver
To:     Tim Harvey <tharvey@gateworks.com>
Cc:     linux-media <linux-media@vger.kernel.org>,
        alsa-devel@alsa-project.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, Shawn Guo <shawnguo@kernel.org>,
        Steve Longerbeam <slongerbeam@gmail.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Hans Verkuil <hansverk@cisco.com>,
        Mauro Carvalho Chehab <mchehab@s-opensource.com>
References: <1514491789-8697-1-git-send-email-tharvey@gateworks.com>
 <1514491789-8697-5-git-send-email-tharvey@gateworks.com>
 <1e65ee61-f282-4b53-dd03-68a89a91da8e@xs4all.nl>
 <CAJ+vNU1ysHuzqOnL4sf3hFZrU5kyGnQ0dFkRObVjCa=NyLsJug@mail.gmail.com>
From:   Hans Verkuil <hverkuil@xs4all.nl>
Message-ID: <517f8b12-e10e-1e8d-6d98-26f5fefe62b8@xs4all.nl>
Date:   Mon, 29 Jan 2018 13:00:48 +0100
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On 01/25/2018 05:15 PM, Tim Harvey wrote:
> On Mon, Jan 15, 2018 at 4:56 AM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>> On 12/28/2017 09:09 PM, Tim Harvey wrote:
>>> Add support for the TDA1997x HDMI receivers.
>>>
>>
>> This looks good.
>>
>> But there is one corner case that isn't handled in this driver: what if there
>> is no AVI InfoFrame (e.g. you receive a DVI signal)?
>>
>> The CTA-861 spec says that in the absence of an AVI InfoFrame you should use
>> limited range for CE formats and full range for IT formats. However, without
>> an AVI InfoFrame it is hard to detect a CE format since there is no VIC code.
>> In addition, a real DVI source will always transmit full range.
>>
>> I would recommend that in the absence of an AVI InfoFrame you fall back to
>> sRGB with full range quantization. Not quite according to the spec but more
>> likely to work in practice.
>>
> 
> Hans,
> 
> Sounds like we are just talking about the default settings which would
> be used in the case of no infoframes. I'll default the struct
> v4l2_hdmi_colorimetry I store in the state struct as:
> 
> +       /*
> +        * default to SRGB full range quantization
> +        * (in case we don't get an infoframe such as DVI signal
> +        */
> +       state->colorimetry.colorspace = V4L2_COLORSPACE_SRGB;
> +       state->colorimetry.quantization = V4L2_QUANTIZATION_FULL_RANGE;
> +

I agree.

> 
> 
>>> <snip>
>>> +static int tda1997x_enum_mbus_code(struct v4l2_subdev *sd,
>>> +                               struct v4l2_subdev_pad_config *cfg,
>>> +                               struct v4l2_subdev_mbus_code_enum *code)
>>> +{
>>> +     struct tda1997x_state *state = to_state(sd);
>>> +
>>> +     if (code->index > 0)
>>> +             return -EINVAL;
>>> +
>>> +     code->code = state->code;
>>
>> Hmm. This receiver supports multiple output formats, but you advertise only one.
>> That looks wrong. If nothing else, you should be able to switch between RGB and
>> YUV 4:4:4 since they use the same port config.
>>
>> It's a common use-case that you want to switch between RGB and YUV depending on
>> the source material (i.e. if you receive a desktop/graphics then RGB is best, if
>> you receive video then YUV 4:2:2 or 4:2:0 is best).
>>
>> Hardcoding just one format won't do.
>>
> 
> I've been thinking about this a bit. I had hard-coded a single format
> for now because I haven't had any good ideas on how to deal with the
> fact that the port mappings would need to differ if you change from
> the RGB888/YUV444 (I think these are referred to as 'planar' formats?)
> to YUV422 (semi-planar) and BT656 formats. It is true though that the
> 36bit (TDA19973) RGB888/YUV444 and 24bit (TDA19971/2) formats can both
> be supported with the same port mappings / pinout.

Regarding terminology:

RGB and YUV are typically interleaved, i.e. the color components are
(for two pixels) either RGBRGB for RGB888, YUVYUV for YUV444 or YUYV
for YUV422.

Planar formats are in practice only seen for YUV and will first output
all Y samples, and then the UV samples. This requires that the hardware
buffers the frame and that's not normally done by HDMI receivers.

The DMA engine, however, is often able to split up the interleaved YUV
samples that it receives and DMA them to separate buffers, thus turning
an interleaved media bus format to a planar memory format.

BT656 doesn't refer to how the samples are transferred, instead it
refers to how the hsync and vsync are reported. The enum v4l2_mbus_type
has various options, one of them being BT656.

Which mbus type is used is board specific (and should come from the
device tree). Whether to transmit RGB888, YUV444 or YUV422 (or possibly
even YUV420) is dynamic and is up to userspace since it is use-case
dependent.

So you'll never switch between BT656 and CSI, but you can switch between
BT656+RGB and BT656+YUV, or between CSI+RGB and CSI+YUV.

> 
> For example the GW5400 has a TDA19971 mapped to IMX6 CSI_DATA[19:4]
> (16bit) for YUV422. However if you want to use BT656 you have to shift
> the TDA19971 port mappings to get the YCbCr pins mapped to
> CSI_DATA[19:x] and those pin groups are at the bottom of the bus for
> the RGB888/YUV444 format.

As mentioned above, you wouldn't switch between mbus types.

> 
> I suppose however that perhaps for the example above if I have a 16bit
> width required to support YUV422 there would never be a useful case
> for supporting 8-bit/10-bit/12-bit BT656 on the same board?

You wouldn't switch between mbus types, but if the device tree configures
BT.656 with a bus width of 24 bits, then the application might very well
want to dynamically switch between 8, 10 and 12 bits per color component.

> 
> Maybe I can define an array of mbus_codes in the state structure then
> fill in the possible states per bit width during init like this:
> 
>         switch (state->info->type) {
>         case TDA19973:
>                 switch (pdata->vidout_bus_width) {
>                 case 36:
>                         /* 36bit YUV */
>                         state->mbus_codes[0] = MEDIA_BUS_FMT_YUV12_1X36;
>                         /* 36bit RGB */
>                         state->mbus_codes[1] = MEDIA_BUS_FMT_RGB121212_1X36;
>                         break;
>                 case 24:
>                         /* 24bit BT656 (YUV422 semi-planar: 1-cycle) */
>                         state->mbus_codes[0] = MEDIA_BUS_FMT_UYVY12_1X24;
>                         /* 24bit YUV */
>                         state->mbus_codes[1] = MEDIA_BUS_FMT_YUV8_1X24;
>                         break;
>                 case 12:
>                         /* 12bit BT656 (2-cycle) */
>                         state->mbus_codes[0] = MEDIA_BUS_FMT_UYVY12_2X12;
>                         break;
>                 }
>                 break;
>         case TDA19971:
>                 switch (pdata->vidout_bus_width) {
>                 case 24:
>                         /* 24bit YUV */
>                         state->mbus_codes[0] = MEDIA_BUS_FMT_YUV8_1X24;
>                         /* 24bit RGB */
>                         state->mbus_codes[1] = MEDIA_BUS_FMT_RGB888_1X24;
>                         break;
>                 case 20: /* 20bit YUV422 */
>                         state->mbus_codes[0] = MEDIA_BUS_FMT_UYVY10_1X20;
>                         break;
>                 case 16: /* 16bit BT656 (YUV422 semi-planar: 1-cycle) */
>                         state->mbus_codes[0] = MEDIA_BUS_FMT_UYVY8_1X16;
>                         break;
>                 case 12: /* 12bit BT656 (2-cycle) */
>                         state->mbus_codes[0] = MEDIA_BUS_FMT_UYVY12_2X12;
>                         break;
>                 case 10: /* 10bit BT656 (2-cycle) */
>                         state->mbus_codes[0] = MEDIA_BUS_FMT_UYVY10_2X10;
>                         break;
>                 case 8: /* 8bit BT656 (2-cycle) */
>                         state->mbus_codes[0] = MEDIA_BUS_FMT_UYVY8_2X8;
>                         break;
>                 }
>         }
>         /* default format */
>         state->mbus_code = state->mbus_codes[0];
> 
> This doesn't support the fact for example that a 20bit bus can also
> support the 8/10/12bit BT656 formats.

You probably need to add a layer in between:

	switch (state->info->type) {
	case TDAXXXX:
		switch (mbus_type) {
		case BT656:
			switch (bus_width) {
			case 24:
				add support for 8, 10 and 12 bit mbus_codes,
				and whatever else can be supported by this width.

> 
>>> +
>>> +     return 0;
>>> +}
>>> +
>>> +static int tda1997x_fill_format(struct tda1997x_state *state,
>>> +                             struct v4l2_mbus_framefmt *format)
>>> +{
>>> +     const struct v4l2_bt_timings *bt;
>>> +
>>> +     v4l_dbg(1, debug, state->client, "%s\n", __func__);
>>> +
>>> +     if (!state->detected_timings)
>>> +             return -EINVAL;
>>> +
>>> +     memset(format, 0, sizeof(*format));
>>> +     bt = &state->detected_timings->bt;
>>> +     format->width = bt->width;
>>> +     format->height = bt->height;
>>> +     format->colorspace = state->colorimetry.colorspace;
>>> +
>>> +     return 0;
>>> +}
>>> +
>>> +static int tda1997x_get_pad_format(struct v4l2_subdev *sd,
>>> +                                struct v4l2_subdev_pad_config *cfg,
>>> +                                struct v4l2_subdev_format *format)
>>> +{
>>> +     struct tda1997x_state *state = to_state(sd);
>>> +
>>> +     v4l_dbg(1, debug, state->client, "%s\n", __func__);
>>> +     if (format->pad != TDA1997X_PAD_SOURCE)
>>> +             return -EINVAL;
>>> +
>>> +     tda1997x_fill_format(state, &format->format);
>>> +
>>> +     if (format->which == V4L2_SUBDEV_FORMAT_TRY) {
>>> +             struct v4l2_mbus_framefmt *fmt;
>>> +
>>> +             fmt = v4l2_subdev_get_try_format(sd, cfg, format->pad);
>>> +             format->format.code = format->format.code;
>>> +     } else
>>> +             format->format.code = state->code;
>>
>> No need to mess around with TRY vs ACTIVE. The behavior is the same for
>> both.
> 
> only if I have a single bus format though right?

Yes, that's correct.

> 
>>
>>> +
>>> +     return 0;
>>> +}
>>> +
>>> +static int tda1997x_set_pad_format(struct v4l2_subdev *sd,
>>> +                                struct v4l2_subdev_pad_config *cfg,
>>> +                                struct v4l2_subdev_format *format)
>>> +{
>>> +     struct v4l2_mbus_framefmt *fmt;
>>> +
>>> +     if (format->pad != TDA1997X_PAD_SOURCE)
>>> +             return -EINVAL;
>>> +
>>> +     if (format->which == V4L2_SUBDEV_FORMAT_ACTIVE)
>>> +             return tda1997x_get_pad_format(sd, cfg, format);
>>
>> Same here, just call return tda1997x_get_pad_format(sd, cfg, format);
>>
>> But note that it makes no sense to support only one possible mbus code
>> when it is clearly possible to switch between multiple output formats.
>>
>> I'm not sure why I didn't see that earlier...
>>
> 
> But once I add in the multiple mbus formats then I need the try vs
> active correct?

Yes.

Regards,

	Hans