linux-kernel - Re: [PATCH v2] arm64: dts: rockchip: Adjust the HDMI DDC IO driver strength for rk3588

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Message-ID: <3704844.aeNJFYEL58@workhorse>
Date: Tue, 27 May 2025 13:53:56 +0200
From: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
To: heiko@...ech.de, linux-rockchip@...ts.infradead.org,
 Andy Yan <andyshrk@....com>
Cc: simic@...jaro.org, krzk+dt@...nel.org, robh@...nel.org,
 devicetree@...r.kernel.org, conor+dt@...nel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-rockchip@...ts.infradead.org, algea.cao@...k-chips.com,
 Andy Yan <andy.yan@...k-chips.com>
Subject:
 Re: [PATCH v2] arm64: dts: rockchip: Adjust the HDMI DDC IO driver strength
 for rk3588

On Thursday, 22 May 2025 04:05:24 Central European Summer Time Andy Yan wrote:
> From: Andy Yan <andy.yan@...k-chips.com>
> 
> For the RK3588 HDMI controller, the falling edge of DDC SDA and SCL
> almost coincide and cannot be adjusted by HDMI registrer, resulting
> in poor compatibility of DDC communication.
> 
> An improvement of the compatibility of DDC can be done by increasing
> the driver strength of SCL and decreasing the driver strength of SDA
> to increase the slope of the falling edge.
> 
> It should be noted that the maximum driving strength of hdmim0_tx1_scl
> is only 3, which is different from that of the other IOs.
> 
> Signed-off-by: Andy Yan <andy.yan@...k-chips.com>
> 
> ---
> 
> Changes in v2:
> - Correct the max drive level of hdmim0_tx1_scl.
> 
>  .../dts/rockchip/rk3588-base-pinctrl.dtsi     | 20 +++++------
>  .../dts/rockchip/rk3588-extra-pinctrl.dtsi    |  5 +--
>  .../boot/dts/rockchip/rockchip-pinconf.dtsi   | 35 +++++++++++++++++++
>  3 files changed, 48 insertions(+), 12 deletions(-)
> 

Tested-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>

Quickly tested this on both HDMI ports of a ROCK 5T with an HDMI capture
card on the other end. While I didn't originally have any issues to begin
with, this patch does not introduce any new ones, so seems good to me.