linux-kernel - Re: [PATCH 2/8] drm/loongson: Introduce a drm bridge driver for it66121 HDMI transmitter

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Date:   Mon, 30 Oct 2023 11:13:58 +0100
From:   Maxime Ripard <mripard@...nel.org>
To:     Sui Jingfeng <suijingfeng@...ngson.cn>
Cc:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 2/8] drm/loongson: Introduce a drm bridge driver for
 it66121 HDMI transmitter

Hi,

On Mon, Oct 30, 2023 at 05:42:28PM +0800, Sui Jingfeng wrote:
> On 2023/10/30 06:53, Dmitry Baryshkov wrote:
> > On Sun, 29 Oct 2023 at 21:46, Sui Jingfeng <suijingfeng@...ngson.cn> wrote:
> > > The IT66121 is a DVO to HDMI converter, LS3A5000+LS7A1000 ML5A_MB use this
> > > chip to support HDMI output. Thus add a drm bridge based driver for it.
> > > This patch is developed with drivers/gpu/drm/bridge/ite-it66121.c as base.
> > Please use the original bridge driver instead of adding a new one.

FTR I agree with Dmitry here, duplicating drivers because it's easier is
a show-stopper

> I'm agree with the spirit of code sharing, but this is nearly
> impossible for non-DT system.
> 
> Because the original bridge driver(say it66121.ko) is fully dependent
> on the DT. UEFI+ACPI based system can not use with it.
>
> Our I2C adapter is created by the drm/loongson.ko on the runtime.
> The potential problem is that *cyclic dependency* !
> 
> I2C adapter driver is depend on drm/loongson
> drm/loongson depend on drm bridge driver (say it66121.ko)
> drm bridge driver (say it66121.ko) depend on I2C adapter to setup.
>
> This plus the defer probe mechanism is totally a trap,
> incurring troubles and don't work.

I'm sure all those issues can be fixed :)

Maxime

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