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Subject: Re: [PATCH v4 02/10] drm/ingenic: Add support for JZ4780 and HDMI
 output
From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <VM970R.TLCBMNA67DOI2@crapouillou.net>
Date:   Wed, 29 Sep 2021 16:42:10 +0200
Cc:     Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Kees Cook <keescook@chromium.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrzej Hajda <a.hajda@samsung.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Robert Foss <robert.foss@linaro.org>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        Harry Wentland <harry.wentland@amd.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        Maxime Ripard <maxime@cerno.tech>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        Paul Boddie <paul@boddie.org.uk>, devicetree@vger.kernel.org,
        linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
        letux-kernel@openphoenux.org, Jonas Karlman <jonas@kwiboo.se>,
        dri-devel@lists.freedesktop.org
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To:     Paul Cercueil <paul@crapouillou.net>
Precedence: bulk

Hi Paul,

> Am 29.09.2021 um 16:30 schrieb Paul Cercueil <paul@crapouillou.net>:
>=20
> Hi,
>=20
> Le mar., sept. 28 2021 at 14:06:03 +0200, H. Nikolaus Schaller =
<hns@goldelico.com> a =C3=A9crit :
>> 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 =3D =
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?
>=20
> 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.

>=20
>>> 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.
>=20
> 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