linux-kernel - Re: [PATCH 7/8] usb: typec: ucsi: glink: merge pmic_glink

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Date: Thu, 16 May 2024 11:18:20 +0300
From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH 7/8] usb: typec: ucsi: glink: merge pmic_glink_altmode
 driver

Hi Dmitry,

On Wed, May 15, 2024 at 06:01:48PM +0300, Dmitry Baryshkov wrote:
> > I have played with the DP AltMode driver. I got it somewhat working,
> > but I think I'm facing a control issue.
> > Basically, the altmode driver wants to control pin assignment on its
> > own. It works with the software TCPM, as we control it.
> > It works with the normal UCSI, because it still can configure pin
> > config. However with PMIC GLINK implementation there is no way to
> > control pin assignment from the Linux side. The firmware does that for
> > us.
> > What would be the recommended way to handle it? Is it okay to override
> > status_update to return just the selected pin config? Or is there any
> > other (better) way to handle such an issue?
> 
> Any suggestions or further comments? Is it better to extend the
> DisplayPort Altmode driver with the 'forced' transitions? Or it would be
> fine to just register a partner device, emulate the userspace events,
> but completely ignore the existing displayport driver?

I may have to look at the DP alt mode with the TI host interface
(drivers/usb/typec/tipd/) at some point, because on some systems the
firmware does not seem to automatically enter the mode, but the forced
transition option would probable work there as well...

I would prefer that we don't ignore the DP alt mode driver, but just
to be clear, I'm also not completely against it if you feel that would
be the most reasonable option in your case.

br,

-- 
heikki