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Date:   Wed, 29 Sep 2021 15:30:31 +0100
From:   Paul Cercueil <paul@crapouillou.net>
Subject: Re: [PATCH v4 02/10] drm/ingenic: Add support for JZ4780 and HDMI
 output
To:     "H. Nikolaus Schaller" <hns@goldelico.com>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
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        Harry Wentland <harry.wentland@amd.com>,
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        letux-kernel@openphoenux.org, Jonas Karlman <jonas@kwiboo.se>,
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Hi,

Le mar., sept. 28 2021 at 14:06:03 +0200, H. Nikolaus Schaller 
<hns@goldelico.com> a ?crit :
> Hi Paul,
> 
>>  Am 28.09.2021 um 12:21 schrieb H. Nikolaus Schaller 
>> <hns@goldelico.com>:
>> 
>>>>  @@ -1492,10 +1555,16 @@ static int ingenic_drm_init(void)
>>>>  {
>>>>  	int err;
>>>>  +	if (IS_ENABLED(CONFIG_DRM_INGENIC_DW_HDMI)) {
>>>>  +		err = platform_driver_register(ingenic_dw_hdmi_driver_ptr);
>>>>  +		if (err)
>>>>  +			return err;
>>>>  +	}
>>> 
>>>  I don't see why you need to register the ingenic-dw-hdmi driver 
>>> here. Just register it in the ingenic-dw-hdmi driver.
>> 
>>  Ok, I never though about this (as the code was not from me). We 
>> apparently just followed the IPU code pattern (learning by example).
>> 
>>  It indeed looks not necessary and would also avoid the 
>> ingenic_dw_hdmi_driver_ptr dependency.
>> 
>>  But: what is ingenic_ipu_driver_ptr then good for?
>> 

It's done this way because ingenic-drm-drv.c and ingenic-ipu.c are both 
compiled within the same module ingenic-drm.

I'm not sure this is still required, maybe ingenic-ipu.c can be its own 
module now.

>> 
>>  If we can get rid of this as well, we can drop patch 1/10 
>> ("drm/ingenic: Fix drm_init error path if IPU was registered") 
>> completely.
> 
> A quick test shows that it *is* required. At least if I configure 
> everything as modules.
> But like you I can't explain why.

Well, a quick test here shows that it is not required, at least when 
configuring with everything built-in.

-Paul

> Well, just a very rough idea (may be wrong): the bridge chain is not 
> like an i2c bus and
> clients are not automatically loaded/probed if linked in the device 
> tree. Therefore the
> consumer (ingenic_drm_drv) must register the "clients" like IPU and 
> HDMI.
> 
> BR,
> Nikolaus
>