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

[Mateusz Kwiatkowski]

W dniu 9.09.2022 o 11:46, Maxime Ripard pisze:
> On Wed, Sep 07, 2022 at 09:52:09PM +0200, Mateusz Kwiatkowski wrote:
>> 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.
>
> Ack
>
>>>>> +/**
>>>>> + * 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?
>
> This is the way we're usually documenting it in DRM:
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_plane.c#L357
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_crtc.c#L861
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_blend.c#L546
>
> So I'd rather keep it consistent
>
> Maxime

Ack, OK then.