linux-kernel - Re: [PATCH v6 2/2] usb: typec: Add support for Parade PS8830 Type-C Retimer

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Message-ID: <Z7SQk2UmuXo3jfBQ@hovoldconsulting.com>
Date: Tue, 18 Feb 2025 14:52:19 +0100
From: Johan Hovold <johan@...nel.org>
To: Stephan Gerhold <stephan.gerhold@...aro.org>
Cc: 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>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Rajendra Nayak <quic_rjendra@...cinc.com>,
	Sibi Sankar <quic_sibis@...cinc.com>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Trilok Soni <quic_tsoni@...cinc.com>,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v6 2/2] usb: typec: Add support for Parade PS8830 Type-C
 Retimer

On Tue, Feb 18, 2025 at 10:26:58AM +0100, Stephan Gerhold wrote:
> On Tue, Feb 18, 2025 at 08:54:47AM +0100, Johan Hovold wrote:
> > On Fri, Feb 14, 2025 at 09:52:33AM +0100, Johan Hovold wrote:
> > > On Thu, Feb 06, 2025 at 11:28:28AM +0200, 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.
> > [...]
> > > > +	/* skip resetting if already configured */
> > > > +	if (regmap_test_bits(retimer->regmap, REG_USB_PORT_CONN_STATUS_0,
> > > > +			     CONN_STATUS_0_CONNECTION_PRESENT) == 1)
> > > > +		return gpiod_direction_output(retimer->reset_gpio, 0);
> > > 
> > > I'm still a little concerned about this. Won't you end up with i2c
> > > timeout errors in the logs if the device is held in reset before probe?
> > 
> > You should be able to use i2c_smbus_read_byte() to avoid logging errors
> > when the boot firmware has *not* enabled the device.
> 
> FWIW, regmap_test_bits() doesn't seem to print any errors either, so I
> don't think switching to i2c_smbus_read_byte() is necessary.

Thanks for checking.

> Since I was curious, I tried booting the X1E80100 with
>  1. One PS8830 instance left as-is
>  2. One PS8830 instance changed to invalid I2C address
>  3. One PS8830 instance changed to have reset pin asserted via pinctrl
> 
> There are no errors whatsoever, even for the one with invalid I2C
> address. In other words, the slightly more concerning part is that the
> driver doesn't check that any of the regmap reads/writes actually
> succeed.

Indeed.
 
> The diff I used for testing is below. (1) prints "skipping reset", (2)
> and (3) print "continuing reset".

And thanks for confirming.

I've found a few more issues that should be addressed so I'm preparing
follow-up series.

Johan