Re: [PATCH v5 2/8] dt-bindings: phy: rockchip,rk3588-mipi-dcphy: Add a cell to select TX or RX

From: Rob Herring <robh@kernel.org>
To: 楊智成 <jason98166@gmail.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>,
	Vinod Koul <vkoul@kernel.org>,
	Neil Armstrong <neil.armstrong@linaro.org>,
	Manivannan Sadhasivam <mani@kernel.org>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Heiko Stuebner <heiko@sntech.de>,
	Guochun Huang <hero.huang@rock-chips.com>,
	Philipp Zabel <p.zabel@pengutronix.de>,
	Michael Riesch <michael.riesch@collabora.com>,
	Sebastian Reichel <sebastian.reichel@collabora.com>,
	Bryan O'Donoghue <bryan.odonoghue@linaro.org>,
	linux-phy@lists.infradead.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 2/8] dt-bindings: phy: rockchip,rk3588-mipi-dcphy: Add a cell to select TX or RX
Date: Mon, 19 Oct 2026 10:06:31 -0500	[thread overview]
Message-ID: <20261019150631.GA265407-robh@kernel.org> (raw)
In-Reply-To: <CAPwA33+bR1BF9KeA9my07Yz7gXW7TXq8EPhwQ4GvHMSFDk+uWw@mail.gmail.com>

On Mon, Oct 19, 2026 at 04:15:03PM +0800, 楊智成 wrote:
> Hi Krzysztof, Rob,
> 
> > Existing OS should ignore surplus cell if the driver is coded properly.
> > Same as adding new properties or new front-compatible.  The question is
> > how the existing driver behaves?
> 
> As you pointed out on 5/8, the xlate checks args_count != 1. The DC-PHY
> driver was merged in v6.15, so every kernel since 6.15 fails on a second cell.
> 
> 1. Keep the second cell. Add the patch as follows:
> 
> - if (args->args_count != 1) {
> + if (args->args_count < 1) {
>     dev_err(dev, "invalid number of arguments\n");
>     return ERR_PTR(-EINVAL);
>   }
> 
> + if (args->args_count > 1 && args->args[1]) {
> +   dev_err(dev, "only the transmitter is supported\n");
> +   return ERR_PTR(-EINVAL);
> + }
> 
>   With Fixes: and Cc: stable, the stable kernels maintained at that
>   time (currently 6.18.y and 7.2.y) keep DSI working with the new
>   dts, and the receiver fails cleanly instead of getting the transmitter.
>   But EOL kernels (6.15, 6.16, 6.17, 6.19, 7.0, 7.1) stay affected.
>   It goes in with the series, since two-cell dts only exist after it.
> 
> 2. Use a flag in the upper bits of the existing cell, as Rob
>     suggested. Existing kernels are not affected, unless a board enables
>     the DC-PHY CSI-2 receiver on 7.0 or later without this series.
> 
> I will write the impact clearly whichever  approach is selected in
> the related commit messages and the cover letter.
> 
> I think the cell approach is easier to read and more symmetric in the
> long term,
> but it breaks more. Which one do you think is better? Thanks.

I'm not a user of this platform, so I don't care. Up to the platform 
maintainers to decide if breakage is acceptible. You just need to 
document the issue in the commit message.

Rob

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