Re: [PATCH v2 09/41] drm/connector: Add TV standard property

[Mateusz Kwiatkowski <kfyatek@gmail.com>]

Hi Maxime,

W dniu 7.09.2022 o 14:10, Maxime Ripard pisze:
> Hi,
>
> On Fri, Sep 02, 2022 at 12:00:33AM +0200, Mateusz Kwiatkowski wrote:
>> W dniu 29.08.2022 o 15:11, Maxime Ripard pisze:
>>> The TV mode property has been around for a while now to select and get the
>>> current TV mode output on an analog TV connector.
>>>
>>> Despite that property name being generic, its content isn't and has been
>>> driver-specific which makes it hard to build any generic behaviour on top
>>> of it, both in kernel and user-space.
>>>
>>> Let's create a new bitmask tv norm property, that can contain any of the
>>> analog TV standards currently supported by kernel drivers. Each driver can
>>> then pass in a bitmask of the modes it supports.
>>
>> This is not a bitmask property anymore, you've just changed it to an enum.
>> The commit message is now misleading.
>>
>>> +static const struct drm_prop_enum_list drm_tv_mode_enum_list[] = {
>>> +    { DRM_MODE_TV_MODE_NTSC_443, "NTSC-443" },
>>> +    { DRM_MODE_TV_MODE_NTSC_J, "NTSC-J" },
>>> +    { DRM_MODE_TV_MODE_NTSC_M, "NTSC-M" },
>>> +    { DRM_MODE_TV_MODE_PAL_60, "PAL-60" },
>>> +    { DRM_MODE_TV_MODE_PAL_B, "PAL-B" },
>>> +    { DRM_MODE_TV_MODE_PAL_D, "PAL-D" },
>>> +    { DRM_MODE_TV_MODE_PAL_G, "PAL-G" },
>>> +    { DRM_MODE_TV_MODE_PAL_H, "PAL-H" },
>>> +    { DRM_MODE_TV_MODE_PAL_I, "PAL-I" },
>>> +    { DRM_MODE_TV_MODE_PAL_M, "PAL-M" },
>>> +    { DRM_MODE_TV_MODE_PAL_N, "PAL-N" },
>>> +    { DRM_MODE_TV_MODE_PAL_NC, "PAL-Nc" },
>>> +    { DRM_MODE_TV_MODE_SECAM_60, "SECAM-60" },
>>> +    { DRM_MODE_TV_MODE_SECAM_B, "SECAM-B" },
>>> +    { DRM_MODE_TV_MODE_SECAM_D, "SECAM-D" },
>>> +    { DRM_MODE_TV_MODE_SECAM_G, "SECAM-G" },
>>> +    { DRM_MODE_TV_MODE_SECAM_K, "SECAM-K" },
>>> +    { DRM_MODE_TV_MODE_SECAM_K1, "SECAM-K1" },
>>> +    { DRM_MODE_TV_MODE_SECAM_L, "SECAM-L" },
>>> +};
>>
>> I did not comment on it the last time, but this list looks a little bit random.
>>
>> Compared to the standards defined by V4L2, you also define SECAM-60 (a good
>> thing to define, because why not), but don't define PAL-B1, PAL-D1, PAL-K,
>> SECAM-H, SECAM-LC (whatever that is - probably just another name for SECAM-L,
>> see my comment about PAL-Nc below), or NTSC-M-KR (a Korean variant of NTSC).
>>
>> Like I mentioned previously, I'm personally not a fan of including all those
>> CCIR/ITU system variants, as they don't mean any difference to the output unless
>> there is an RF modulator involved. But I get it that they have already been used
>> and regressing probably wouldn't be a very good idea. But in that case keeping
>> it consistent with the set of values used by V4L2 would be wise, I think.
>
> Ack. What would be the list of standards we'd absolutely need? NSTC-M,
> NTSC-J, PAL-60, PAL-B, PAL-M, SECAM-60 and SECAM-B?

The "essential list" IMO is NTSC, NTSC-J, NTSC-443, PAL, PAL-M, PAL-N and SECAM.
Note that:

- I intentionally propose "NTSC", "PAL" and "SECAM" without an ITU system
  designation. If we only consider composite signals, there's no difference
  between e.g. PAL-B, PAL-D and PAL-I, so it's better to label it as a generic
  mode, IMO.

  * PAL-M and PAL-N are different, because those unique color encodings were
    only ever used with Systems M and N, respectively.

  * NTSC-J is also different, because "System J" doesn't exist anywhere in ITU
    documents. Japan technically uses System M with a non-standard black level.
    But "NTSC-J" stuck as a universally recognized name for that variant.

- I intentionally did not list PAL-60 or SECAM-60. TBH... PAL-60 is just
  regular PAL paired with 480i60 modeline. Most if not all displays that
  accept PAL-60 input will just label it as "PAL". If we are not introducing
  strict modeline validation, then maybe separating PAL and PAL-60 isn't really
  necessary? Same goes for SECAM vs. SECAM-60.
 
  ...and same goes for NTSC vs. NTSC-50 a.k.a NTSC-N, which is a very exotic
  mode, but known to exist at least in the Atari ST world, see also:
  https://en.wikipedia.org/wiki/NTSC#NTSC-N/NTSC50

Combining PAL and PAL-60 into a single setting would complicate the vc4 driver
a little bit, though, as the registers need to be set up differently for those.

My feelings about the PAL-60 issue are not that strong, though. Merging PAL
and PAL-60 in this context is just a loose suggestion, I won't even try to
argue if you disagree.

>>> +/**
>>> + * drm_mode_create_tv_properties - create TV specific connector properties
>>> + * @dev: DRM device
>>> + * @supported_tv_modes: Bitmask of TV modes supported (See DRM_MODE_TV_MODE_*)
>>> +
>>> + * Called by a driver's TV initialization routine, this function creates
>>> + * the TV specific connector properties for a given device.  Caller is
>>> + * responsible for allocating a list of format names and passing them to
>>> + * this routine.
>>> + *
>>> + * Returns:
>>> + * 0 on success or a negative error code on failure.
>>> + */
>>> +int drm_mode_create_tv_properties(struct drm_device *dev,
>>> +                  unsigned int supported_tv_modes)
>>
>> supported_tv_modes is supposed to be a bitmask of BIT(DRM_MODE_TV_MODE_*)
>> (or (1<<DRM_MODE_TV_MODE_*)) rather than DRM_MODE_TV_MODE_* directly, but this
>> is not said explicitly anywhere in this doc comment.
>
> The argument doc mentions that it's a "Bitmask of TV modes supported
> (See DRM_MODE_TV_MODE_*)", how would you improve it?

Maybe something like "Bitwise OR of BIT(DRM_MODE_TV_MODE_*) values"? Or maybe
just add a little usage example?

> Thanks!
> Maxime

Best regards,
Mateusz Kwiatkowski