linux-kernel - Re: [PATCH 00/14] Add initial support for the Rockchip RK3588 HDMI TX Controller

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Message-ID: <b8066150-c147-4eb6-9f7a-2bd0268c274e@collabora.com>
Date: Tue, 4 Jun 2024 23:33:57 +0300
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: neil.armstrong@...aro.org, Heiko Stuebner <heiko@...ech.de>,
 Andrzej Hajda <andrzej.hajda@...el.com>, Robert Foss <rfoss@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 Sandy Huang <hjc@...k-chips.com>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Mark Yao <markyao0591@...il.com>,
 Andy Yan <andy.yan@...k-chips.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org,
 devicetree@...r.kernel.org, kernel@...labora.com,
 Alexandre ARNOUD <aarnoud@...com>, Luis de Arquer <ldearquer@...il.com>,
 Algea Cao <algea.cao@...k-chips.com>
Subject: Re: [PATCH 00/14] Add initial support for the Rockchip RK3588 HDMI TX
 Controller

On 6/3/24 4:08 PM, neil.armstrong@...aro.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@...z with RGB/YCbCr4:4:4
>>>>> * YCbCr4:2:0 enabling 2160p@...z 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.

> 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