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

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Date:   Wed, 29 Sep 2021 16:42:10 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Paul Cercueil <paul@...pouillou.net>
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 Paul,

> Am 29.09.2021 um 16:30 schrieb Paul Cercueil <paul@...pouillou.net>:
> 
> 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.

Ah, I see. Hadn't checked this.

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

What I have seen is that it has its own compatible record. So there could be load-on-demand by DTS.

> 
>>> 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.

IMHO the hdmi driver (module) should be loaded on demand. Not everyone wants to have it.

Well, that is the problem that needs to be solved...

BR and thanks,
Nikolaus