Message-ID: <CAJ+vNU22eAwxLFNjsj96Spgi9qLwpWpEk7A2dJy50L8LyW_uCQ@mail.gmail.com>
Date:   Wed, 14 Feb 2018 07:46:41 -0800
From:   Tim Harvey <tharvey@...eworks.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     linux-media <linux-media@...r.kernel.org>,
        alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Shawn Guo <shawnguo@...nel.org>,
        Steve Longerbeam <slongerbeam@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Hans Verkuil <hansverk@...co.com>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>
Subject: Re: [PATCH v10 6/8] media: i2c: Add TDA1997x HDMI receiver driver

On Wed, Feb 14, 2018 at 6:08 AM, Hans Verkuil <hverkuil@...all.nl> wrote:
> Hi Tim,
>
> On 12/02/18 23:27, Tim Harvey wrote:
>> On Fri, Feb 9, 2018 at 12:08 AM, Hans Verkuil <hverkuil@...all.nl> wrote:
>>> Hi Tim,
>>>
>>> We're almost there. Two more comments:
>>>
>>> On 02/09/2018 07:32 AM, Tim Harvey wrote:
>>>> +static int
>>>> +tda1997x_detect_std(struct tda1997x_state *state,
>>>> +                 struct v4l2_dv_timings *timings)
>>>> +{
>>>> +     struct v4l2_subdev *sd = &state->sd;
>>>> +     u32 vper;
>>>> +     u16 hper;
>>>> +     u16 hsper;
>>>> +     int i;
>>>> +
>>>> +     /*
>>>> +      * Read the FMT registers
>>>> +      *   REG_V_PER: Period of a frame (or two fields) in MCLK(27MHz) cycles
>>>> +      *   REG_H_PER: Period of a line in MCLK(27MHz) cycles
>>>> +      *   REG_HS_WIDTH: Period of horiz sync pulse in MCLK(27MHz) cycles
>>>> +      */
>>>> +     vper = io_read24(sd, REG_V_PER) & MASK_VPER;
>>>> +     hper = io_read16(sd, REG_H_PER) & MASK_HPER;
>>>> +     hsper = io_read16(sd, REG_HS_WIDTH) & MASK_HSWIDTH;
>>>> +     if (!vper || !hper || !hsper)
>>>> +             return -ENOLINK;
>>>
>>> See my comment for g_input_status below. This condition looks more like a
>>> ENOLCK.
>>>
>>> Or perhaps it should be:
>>>
>>>         if (!vper && !hper && !hsper)
>>>                 return -ENOLINK;
>>>         if (!vper || !hper || !hsper)
>>>                 return -ENOLCK;
>>>
>>> I would recommend that you test a bit with no signal and a bad signal (perhaps
>>> one that uses a pixelclock that is too high for this device?).
>>
>> I can't figure out how to produce a signal that can't be locked onto
>> with what I have available.
>
> Are you using a signal generator or just a laptop or something similar as the
> source?
>
> Without a good signal generator it is tricky to test this. A very long HDMI
> cable would likely do it. But for 1080p60 you probably need 20 meters or
> more.
>

I'm using a Marshall V-SG4K-HDI
(http://www.lcdracks.com/racks/DLW/V-SG4K-HDI-signal-generator.php).
It does support 'user defined timings' (see
http://www.lcdracks.com/racks/pdf-pages/instruction_sheets/V-SG4K-HDI_Manual-web.pdf
Timings Details Menu page) and it looks like the max pixel-clock is
300MHz so perhaps I can create a timing that can't be locked onto that
way.

The TDA19971 datasheet
(http://tharvey/src/nxp/tda1997x/TDA19971-datasheet-rev3.pdf) says it
supports:
- All HDTV formats up to 1920x1080p at 50/60 Hz with support for
reduced blanking
- 3D formats including all primary formats up to 1920x1080p at 30 Hz
Frame Packing and 1920x1080p at 60 Hz Side-by-Side and Top-and-Bottom
- PC formats up to UXGA (1600x1200p at 60 Hz) and WUXGA (1920x1200p at 60 Hz)

>>
<snip>
>>>
>>>> +static int
>>>> +tda1997x_g_input_status(struct v4l2_subdev *sd, u32 *status)
>>>> +{
>>>> +     struct tda1997x_state *state = to_state(sd);
>>>> +     u32 vper;
>>>> +     u16 hper;
>>>> +     u16 hsper;
>>>> +
>>>> +     mutex_lock(&state->lock);
>>>> +     v4l2_dbg(1, debug, sd, "inputs:%d/%d\n",
>>>> +              state->input_detect[0], state->input_detect[1]);
>>>> +     if (state->input_detect[0] || state->input_detect[1])
>>>
>>> I'm confused. This device has two HDMI inputs?
>>>
>>> Does 'detecting input' equate to 'I see a signal and I am locked'?
>>> I gather from the irq function that sets these values that it is closer
>>> to 'I see a signal' and that 'I am locked' is something you would test
>>> by looking at the vper/hper/hsper.
>>
>> The TDA19972 and/or TDA19973 has an A and B input but only a single
>> output. I'm not entirely clear if/how to select between the two and I
>> don't have proper documentation for the three chips.
>>
>> The TDA19971 which I have on my board only has 1 input which is
>> reported as the 'A' input. I can likely nuke the stuff looking at the
>> B input and/or put some qualifiers around it but I didn't want to
>> remove code that was derived from some vendor code that might help
>> support the other chips in the future. So I would rather like to leave
>> the 'if A or B' stuff.
>
> OK. Can you add a comment somewhere in the driver about this?
>
> It sounds like it is similar to what the adv7604 has: several inputs but
> only one is used for streaming. But the EDID is made available on both inputs.
>

sure, I will comment about it. I believe that is the way the it works as well.

>>>
>>>> +             *status = 0;
>>>> +     else {
>>>> +             vper = io_read24(sd, REG_V_PER) & MASK_VPER;
>>>> +             hper = io_read16(sd, REG_H_PER) & MASK_HPER;
>>>> +             hsper = io_read16(sd, REG_HS_WIDTH) & MASK_HSWIDTH;
>>>> +             v4l2_dbg(1, debug, sd, "timings:%d/%d/%d\n", vper, hper, hsper);
>>>> +             if (!vper || !hper || !hsper)
>>>> +                     *status |= V4L2_IN_ST_NO_SYNC;
>>>> +             else
>>>> +                     *status |= V4L2_IN_ST_NO_SIGNAL;
>>>
>>> So if we have valid vper, hper and hsper, then there is no signal? That doesn't
>>> make sense.
>>>
>>> I'd expect to see something like this:
>>>
>>>         if (!input_detect[0] && !input_detect[1])
>>>                 // no signal
>>>         else if (!vper || !hper || !vsper)
>>>                 // no sync
>>>         else
>>>                 // have signal and sync
>>
>> sure... reads a bit cleaner. I can't guarantee that any of
>> vper/hper/vsper will be 0 if a signal can't be locked onto without
>> proper documentation or ability to generate such a signal. I do know
>> if I yank the source I get non-zero random values and must rely on the
>> input_detect logic.
>
> Add a comment about this as well. It's good to be clear that this code
> is partially guesswork and partially based on testing.

ok

>
>>
>>>
>>> I'm not sure about the precise meaning of input_detect, so I might be wrong about
>>> that bit.
>>
>> ya... me either. I'm trying my hardest to get this driver up to shape
>> but the documentation I have is utter crap and I'm doing some guessing
>> as well as to what all the registers are and what the meaning of the
>> very obfuscated vendor code does.
>>
>> would you object to detecting timings and displaying via v4l2_dbg when
>> a resolution change is detected (just not 'using' those timings for
>> anything?):
>
> No, not at all. Also useful is to log the detected timings in the log_status
> call. It is *very* handy when testing.
>
> I.e. if 'v4l2-ctl --log-status' gives you both the configured timings and the
> detected timings, then that makes it much easier to debug the driver.
>

ok

>>
>> @@ -1384,6 +1386,7 @@ static void tda1997x_irq_sus(struct tda1997x_state *state,
>>  u8 *flags)
>>                         v4l_err(state->client, "BAD SUS STATUS\n");
>>                         return;
>>                 }
>> +               if (debug)
>> +                              tda1997x_detect_std(state, NULL);
>>                 /* notify user of change in resolution */
>>                 v4l2_subdev_notify_event(&state->sd, &tda1997x_ev_fmt);
>>         }
>>
>> @@ -1140,16 +1140,18 @@ tda1997x_detect_std(struct tda1997x_state *state,
>>                 /* hsmatch matches the hswidth */
>>                 hsmatch = ((hsper <= hsmax) && (hsper >= hsmin)) ? 1 : 0;
>>                 if (hmatch && vmatch && hsmatch) {
>> -                       *timings = v4l2_dv_timings_presets[i];
>>                         v4l2_print_dv_timings(sd->name, "Detected format: ",
>> -                                             timings, false);
>> +                                             &v4l2_dv_timings_presets[i],
>> +                                             false);
>> +                       if (timings)
>> +                               *timings = v4l2_dv_timings_presets[i];
>>                         return 0;
>>                 }
>>         }
>>
>> It seems to make sense to me to be seeing a kernel message when
>> timings change and what they change to without having to query :)
>
> Right.
>
> I'll wait for v11 and I'll make a pull request for it.
>

hopefully I'll get to v11 later today.

Thanks!

Tim

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