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 17:42:28 +0800
From:   Sui Jingfeng <suijingfeng@...ngson.cn>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Maxime Ripard <mripard@...nel.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 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.

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.


>   If
> it needs to be changed in any way, please help everyone else by
> improving it instead of introducing new driver.
>
>> Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
>> ---
>>   drivers/gpu/drm/loongson/Kconfig            |   1 +
>>   drivers/gpu/drm/loongson/Makefile           |   2 +
>>   drivers/gpu/drm/loongson/ite_it66121.c      | 749 ++++++++++++++++++++
>>   drivers/gpu/drm/loongson/ite_it66121.h      |  19 +
>>   drivers/gpu/drm/loongson/ite_it66121_regs.h | 268 +++++++
>>   5 files changed, 1039 insertions(+)
>>   create mode 100644 drivers/gpu/drm/loongson/ite_it66121.c
>>   create mode 100644 drivers/gpu/drm/loongson/ite_it66121.h
>>   create mode 100644 drivers/gpu/drm/loongson/ite_it66121_regs.h
>