Re: [PATCH 1/3] drm/i915: Convert intel_tv connector properties to atomic.

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 13-03-17 om 11:55 schreef Ville Syrjälä:
> On Mon, Mar 13, 2017 at 11:38:33AM +0100, Maarten Lankhorst wrote:
>> Op 13-03-17 om 10:29 schreef Ville Syrjälä:
>>> On Mon, Mar 13, 2017 at 10:22:51AM +0100, Maarten Lankhorst wrote:
>>>> Op 09-03-17 om 18:36 schreef Ville Syrjälä:
>>>>> On Thu, Mar 09, 2017 at 02:06:15PM +0100, Maarten Lankhorst wrote:
>>>>>> As a proof of concept, first try to convert intel_tv, which is a rarely
>>>>>> used connector. It has 5 properties, tv format and 4 margins.
>>>>> Since it's so rare, if you want someone to actually test the code
>>>>> it'll probably make sense to pick another connector ;)
>>>> Yeah but the properties are among the most annoying, with the self modifying code and using state in mode_detect().
>>>>>> I'm less certain about the state behavior itself, should we pass a size
>>>>>> parameter to intel_connector_alloc instead, so duplicate_state
>>>>>> can be done globally if it can be blindly copied?
>>>>>>
>>>>>> Can we also have a atomic_check function for connectors, so the
>>>>>> crtc_state->connectors_changed can be set there? It would be cleaner
>>>>>> and more atomic-like.
>>>>> Hmm. I think it migth be really useful only if we have some
>>>>> interactions between multiple properties that really need to be
>>>>> checked. We might have those already I suppose but we don't seem
>>>>> to check any of it currently. So as a first step I guess we can
>>>>> just keep ignoring any such issues.
>>>> Well it might be, for example not all properties may be set yet so you can only do a sane check in a separate step.
>>>>>> To match the legacy behavior, format can be changed by probing just like
>>>>>> in legacy mode.
>>>>> Self modifying state irks me, but it's what we've been doing so I guess
>>>>> we should keep it.
>>>> Yeah, I hate it too.
>>>>>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>>>>>> ---
>>>>>>  drivers/gpu/drm/i915/intel_tv.c | 238 +++++++++++++++++++++++-----------------
>>>>>>  1 file changed, 136 insertions(+), 102 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
>>>>>> index 6ed1a3ce47b7..0fb1d8621fe8 100644
>>>>>> --- a/drivers/gpu/drm/i915/intel_tv.c
>>>>>> +++ b/drivers/gpu/drm/i915/intel_tv.c
>>>>>> @@ -48,8 +48,6 @@ struct intel_tv {
>>>>>>  	struct intel_encoder base;
>>>>>>  
>>>>>>  	int type;
>>>>>> -	const char *tv_format;
>>>>>> -	int margin[4];
>>>>>>  	u32 save_TV_H_CTL_1;
>>>>>>  	u32 save_TV_H_CTL_2;
>>>>>>  	u32 save_TV_H_CTL_3;
>>>>>> @@ -85,6 +83,16 @@ struct intel_tv {
>>>>>>  	u32 save_TV_CTL;
>>>>>>  };
>>>>>>  
>>>>>> +struct intel_tv_connector_state {
>>>>>> +	struct drm_connector_state base;
>>>>>> +
>>>>>> +	int format;
>>>>>> +	int margin[4];
>>>>>> +};
>>>>>> +
>>>>>> +#define to_intel_tv_connector_state(state) \
>>>>>> +	container_of((state), struct intel_tv_connector_state, base)
>>>>>> +
>>>>>>  struct video_levels {
>>>>>>  	u16 blank, black;
>>>>>>  	u8 burst;
>>>>>> @@ -873,32 +881,18 @@ intel_disable_tv(struct intel_encoder *encoder,
>>>>>>  	I915_WRITE(TV_CTL, I915_READ(TV_CTL) & ~TV_ENC_ENABLE);
>>>>>>  }
>>>>>>  
>>>>>> -static const struct tv_mode *
>>>>>> -intel_tv_mode_lookup(const char *tv_format)
>>>>>> +static const struct tv_mode *intel_tv_mode_find(struct drm_connector_state *conn_state)
>>>>>>  {
>>>>>> -	int i;
>>>>>> +	int format = to_intel_tv_connector_state(conn_state)->format;
>>>>>>  
>>>>>> -	for (i = 0; i < ARRAY_SIZE(tv_modes); i++) {
>>>>>> -		const struct tv_mode *tv_mode = &tv_modes[i];
>>>>>> -
>>>>>> -		if (!strcmp(tv_format, tv_mode->name))
>>>>>> -			return tv_mode;
>>>>>> -	}
>>>>>> -	return NULL;
>>>>>> -}
>>>>>> -
>>>>>> -static const struct tv_mode *
>>>>>> -intel_tv_mode_find(struct intel_tv *intel_tv)
>>>>>> -{
>>>>>> -	return intel_tv_mode_lookup(intel_tv->tv_format);
>>>>>> +	return &tv_modes[format];
>>>>>>  }
>>>>>>  
>>>>>>  static enum drm_mode_status
>>>>>>  intel_tv_mode_valid(struct drm_connector *connector,
>>>>>>  		    struct drm_display_mode *mode)
>>>>>>  {
>>>>>> -	struct intel_tv *intel_tv = intel_attached_tv(connector);
>>>>>> -	const struct tv_mode *tv_mode = intel_tv_mode_find(intel_tv);
>>>>>> +	const struct tv_mode *tv_mode = intel_tv_mode_find(connector->state);
>>>>> It feels a bit fishy to use the state here. Generally that's a no-no.
>>>>> But in this case I wonder if it's the right choice after all. 
>>>>>
>>>>> Not sure if some kind of "automatic" enum value might also work. It
>>>>> would at least avoid the self modifying property problem. Although I
>>>>> wonder if the user would still like to know what was actually used
>>>>> if they chose they automatic mode, so we might need a self modifying
>>>>> RO property for the current mode anyway.
>>>>>
>>>>> But that still leaves the problem of how the user would know which modes
>>>>> they should be able to use if .get_modes()/.mode_valid() doesn't respect
>>>>> the users choice of the tv format. Hmm, tricky. Might be the self
>>>>> modifying property is the only good choice.
>>>>>
>>>>> But if we would use the state here, what's the story with locking going
>>>>> to be? connection_mutex is what protects this stuff, but we're not
>>>>> holding that during mode enumeration.
>>>> Yeah locking is tricky, honestly I have no idea what would be the right thing to do here..
>>>>
>>>> I don't really see a good solution, or at least one that would work correctly with atomic properties.
>>> Maybe we need to keep the format information in both intel_tv and the
>>> state. We'd use the intel_tv->format during detect, and during
>>> duplicate_state we'd do 'state->format = intel_tv->format' and during
>>> commit we'd do 'intel_tv->format = state->format' ?
>>>
>>> Still self modifying, and somewhat racy still, but at least we
>>> shouldn't explode on account of the connector->state dereference.
>>>
>> I thought about that, but where do you want to update it in atomic commit?
> Does it matter? Somewhere around the swap_state I suppose?
>
Hmm, I guess I'll add a connector->set_state hook for this, lets see how far I can get with a less racy v2..

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