linux-kernel - Re: [PATCH v4 2/4] usb: typec: Add support for Parade PS8830 Type-C Retimer

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Message-ID: <ed0c77bd-770c-406d-851f-8589e53cde8b@oss.qualcomm.com>
Date: Sat, 2 Nov 2024 10:17:56 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Abel Vesa <abel.vesa@...aro.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Rajendra Nayak <quic_rjendra@...cinc.com>,
        Sibi Sankar <quic_sibis@...cinc.com>, Johan Hovold <johan@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Trilok Soni <quic_tsoni@...cinc.com>, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v4 2/4] usb: typec: Add support for Parade PS8830 Type-C
 Retimer

On 1.11.2024 5:29 PM, Abel Vesa wrote:
> The Parade PS8830 is a USB4, DisplayPort and Thunderbolt 4 retimer,
> controlled over I2C. It usually sits between a USB/DisplayPort PHY
> and the Type-C connector, and provides orientation and altmode handling.
> 
> The boards that use this retimer are the ones featuring the Qualcomm
> Snapdragon X Elite SoCs.
> 
> Add a driver with support for the following modes:
>  - DisplayPort 4-lanes
>  - DisplayPort 2-lanes + USB3
>  - USB3
> 
> There is another variant of this retimer which is called PS8833. It seems
> to be really similar to the PS8830, so future-proof this driver by
> naming it ps883x.
> 
> Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> ---

[...]

> +static void ps883x_configure(struct ps883x_retimer *retimer, int cfg0, int cfg1, int cfg2)
> +{
> +	regmap_write(retimer->regmap, 0x0, cfg0);
> +	regmap_write(retimer->regmap, 0x1, cfg1);
> +	regmap_write(retimer->regmap, 0x2, cfg2);
> +}

Somewhere between introducing regcache and dropping it, you removed
muxing to a safe mode during _configure()

[...]

> +	/* skip resetting if already configured */
> +	if (regmap_test_bits(retimer->regmap, 0x00, BIT(0)))
> +		return 0;

What is that register and what does BIT(0) mean?

Konrad