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

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Message-ID: <ef1d1796-b45a-4b1b-bb61-4a3c63d3c718@oss.qualcomm.com>
Date: Mon, 4 Nov 2024 11:25:40 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Abel Vesa <abel.vesa@...aro.org>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: 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>, 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 4.11.2024 11:16 AM, Abel Vesa wrote:
> On 24-11-02 10:17:56, Konrad Dybcio wrote:
>> 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()
> 
> Oh, yeah, I forgot to mention that in the change log, it seems.
> 
> Configuring to safe mode is not needed since we always do that on 
> unplug anyway.
> 
>>
>> [...]
>>
>>> +	/* 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?
> 
> Looking at the documentation, the first register is
> REG_USB_PORT_CONN_STATUS and spans over the first 4 bytes.
> 
> But it doesn't really help here.
> 
> BIT(0) doesn't really have a name, it just says "Connection present".

Please define both then. STATUS_CONNECTION_PRESENT sounds good for the bit.

Konrad