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Date: Wed, 5 Jun 2024 11:28:41 +0200
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From: neil.armstrong@linaro.org
Reply-To: neil.armstrong@linaro.org
Subject: Re: [PATCH 00/14] Add initial support for the Rockchip RK3588 HDMI TX
 Controller
To: Andy Yan <andyshrk@163.com>,
 Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Cc: Heiko Stuebner <heiko@sntech.de>, Andrzej Hajda
 <andrzej.hajda@intel.com>, Robert Foss <rfoss@kernel.org>,
 Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
 Jonas Karlman <jonas@kwiboo.se>, Jernej Skrabec <jernej.skrabec@gmail.com>,
 Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
 Maxime Ripard <mripard@kernel.org>, Thomas Zimmermann <tzimmermann@suse.de>,
 David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
 Sandy Huang <hjc@rock-chips.com>, Rob Herring <robh@kernel.org>,
 Krzysztof Kozlowski <krzk+dt@kernel.org>, Conor Dooley
 <conor+dt@kernel.org>, Mark Yao <markyao0591@gmail.com>,
 Andy Yan <andy.yan@rock-chips.com>, dri-devel@lists.freedesktop.org,
 linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
 linux-rockchip@lists.infradead.org, devicetree@vger.kernel.org,
 kernel@collabora.com, Alexandre ARNOUD <aarnoud@me.com>,
 Luis de Arquer <ldearquer@gmail.com>, Algea Cao <algea.cao@rock-chips.com>
References: <20240601-b4-rk3588-bridge-upstream-v1-0-f6203753232b@collabora.com>
 <a4b22708-e85d-448a-8145-244b49bca053@linaro.org>
 <ab0a6372-091b-4293-8907-a4b3ff4845c0@rock-chips.com>
 <11359776.NyiUUSuA9g@phil> <ef60403f-078f-411a-867b-9b551e863f56@linaro.org>
 <b8066150-c147-4eb6-9f7a-2bd0268c274e@collabora.com>
 <4456bc5a.9b2d.18fe7b76790.Coremail.andyshrk@163.com>
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Hi,

On 05/06/2024 11:25, Andy Yan wrote:
> 
> Hi,
> 
> At 2024-06-05 04:33:57, "Cristian Ciocaltea" <cristian.ciocaltea@collabora.com> wrote:
>> On 6/3/24 4:08 PM, neil.armstrong@linaro.org wrote:
>>> Hi,
>>>
>>> On 03/06/2024 15:03, Heiko Stuebner wrote:
>>>> Am Montag, 3. Juni 2024, 14:14:17 CEST schrieb Andy Yan:
>>>>> Hi Neil:
>>>>>
>>>>> On 6/3/24 16:55, Neil Armstrong wrote:
>>>>>> Hi Christian,
>>>>>>
>>>>>> On 01/06/2024 15:12, Cristian Ciocaltea wrote:
>>>>>>> The RK3588 SoC family integrates a Quad-Pixel (QP) variant of the
>>>>>>> Synopsys DesignWare HDMI TX controller used in the previous SoCs.
>>>>>>>
>>>>>>> It is HDMI 2.1 compliant and supports the following features, among
>>>>>>> others:
>>>>>>>
>>>>>> .
>>>>>>
>>>>>> ..
>>>>>>
>>>>>>> * SCDC I2C DDC access
>>>>>>> * TMDS Scrambler enabling 2160p@60Hz with RGB/YCbCr4:4:4
>>>>>>> * YCbCr4:2:0 enabling 2160p@60Hz at lower HDMI link speeds
>>>>>>> * Multi-stream audio
>>>>>>> * Enhanced Audio Return Channel (EARC)
>>>>>> -> Those features were already supported by the HDMI 2.0a compliant
>>>>>> HW, just
>>>>>> list the _new_ features for HDMI 2.1
>>>>>>
>>>>>> I did a quick review of your patchset and I don't understand why you
>>>>>> need
>>>>>> to add a separate dw-hdmi-qp.c since you only need simple variants
>>>>>> of the I2C
>>>>>> bus, infoframe and bridge setup.
>>>>>>
>>>>>> Can you elaborate further ? isn't this Quad-Pixel (QP) TX controller
>>>>>> version
>>>>>> detectable at runtime ?
>>>>>>
>>>>>> I would prefer to keep a single dw-hdmi driver if possible.
>>>>>
>>>>>
>>>>>
>>>>> The QP HDMI controller is a completely different variant with totally
>>>>> different
>>>>> registers layout, see PATCH 13/14.
>>>>> I think make it a separate driver will be easier for development and
>>>>> maintenance.
>>>>
>>>> I'm with Andy here. Trying to navigate a driver for two IP blocks really
>>>> sounds taxing especially when both are so different.
>>
>> Thank you all for the valuable feedback!
>>
>>> I agree, I just wanted more details than "variant of the
>>> Synopsys DesignWare HDMI TX controller", if the register mapping is 100%
>>> different, and does not match at all with the old IP, then it's indeed time
>>> to make a brand new driver, but instead of doing a mix up, it's time to
>>> extract
>>> the dw-hdmi code that could be common helpers into a dw-hdmi-common module
>>> and use them.
>>
>> Sounds good, will handle this in v2.
>>
>>> As I see, no "driver" code can be shared, only DRM plumbings, so perhaps
>>> those
>>> plumbing code should go into the DRM core ?
>>>
>>> In any case, please add more details on the cover letter, including the
>>> detailed
>>> HW differrence and the design you chose so support this new IP.
>>
>> Andy, could you please help with a summary of the HW changes?
>> The information I could provide is rather limited, since I don't have
>> access to any DW IP datasheets and I'm also not familiar enough with the
>> old variant.
>>
>   Accurately, we should refer to it as an entirely new IP，it has nothing in common with
> the current mainline dw-hdmi。 The only  commonality is that they both come from
> Synopsys DesignWare：
> （1）It has a 100% different register mapping
> （2）It supports FRL and DSC
> （3）different configuration flow in many places。
> 
> So I have the same feeling with Heiko and Maxime：
> The DW_HDMI_QP should have a  separate driver and with it's  own CONFIG  such as DRM_DW_HDMI_QP  in Kconfig.
> and the rockchip part should also be split from dw_hdmi-rockchip.c.
> I am sorry we mixed them in dw_hdmi-rockchip.c when we develop the bsp driver，but we really regretted this decision
> when  we repeatedly broke compatibility with dw-hdmi on other socs。

Yes please, and as I say, if there's code common with the old dw-hdmi, please add a common
module if this code can't be moved in core bridge helpers.

Neil

> 
> 
> 
>>> Neil
>>>
>>>>
>>>> Synopsis also created a new dsi controller for the DSI2 standard, with
>>>> a vastly different registers layout.
>>>>
>>>> I guess at some point there is time to say this really is a new IP ;-) .
>>>>
>>>>
>>>> Though while on that thought, I don't fully understand why both a
>>>> compiled
>>>> under the dw_hdmi kconfig symbol. People going for a minimal kernel might
>>>> want one or the other, but not both for their specific board.
>>
>> Indeed, it makes sense to have a dedicated Kconfig option. This is
>> mostly a leftover from downstream implementation, will fix in v2.
>>
>> Thanks again,
>> Cristian
>>
>> _______________________________________________
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>> linux-arm-kernel@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel