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

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Message-ID: <ZyifBejZtb7x0Vyc@linaro.org>
Date: Mon, 4 Nov 2024 12:16:37 +0200
From: Abel Vesa <abel.vesa@...aro.org>
To: 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 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".

> 
> Konrad