linux-kernel - Re: [PATCH v4 02/10] drm/ingenic: Add support for JZ4780 and HDMI output

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Message-Id: <VM970R.TLCBMNA67DOI2@crapouillou.net>
Date:   Wed, 29 Sep 2021 15:30:31 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Kees Cook <keescook@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Harry Wentland <harry.wentland@....com>,
        Sam Ravnborg <sam@...nborg.org>,
        Maxime Ripard <maxime@...no.tech>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Paul Boddie <paul@...die.org.uk>, devicetree@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        letux-kernel@...nphoenux.org, Jonas Karlman <jonas@...boo.se>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v4 02/10] drm/ingenic: Add support for JZ4780 and HDMI
 output

Hi,

Le mar., sept. 28 2021 at 14:06:03 +0200, H. Nikolaus Schaller 
<hns@...delico.com> a écrit :
> Hi Paul,
> 
>>  Am 28.09.2021 um 12:21 schrieb H. Nikolaus Schaller 
>> <hns@...delico.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
>