linux-kernel - Re: [PATCH] usb: typec: altmodes/displayport: Fix probe pin assign check

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Message-ID: <44487e67c4101db4b57090a1ece66974aeab28b9.camel@puri.sm>
Date:   Fri, 17 Feb 2023 12:39:28 +0100
From:   Martin Kepplinger <martin.kepplinger@...i.sm>
To:     Prashant Malani <pmalani@...omium.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Cc:     bleung@...omium.org, stable@...r.kernel.org,
        Diana Zigterman <dzigterman@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guillaume Ranquet <granquet@...libre.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Macpaul Lin <macpaul.lin@...iatek.com>,
        Pablo Sun <pablo.sun@...iatek.com>
Subject: Re: [PATCH] usb: typec: altmodes/displayport: Fix probe pin assign
 check

Am Mittwoch, dem 08.02.2023 um 20:53 +0000 schrieb Prashant Malani:
> While checking Pin Assignments of the port and partner during probe,
> we
> don't take into account whether the peripheral is a plug or
> receptacle.
> 
> This manifests itself in a mode entry failure on certain docks and
> dongles with captive cables. For instance, the Startech.com Type-C to
> DP
> dongle (Model #CDP2DP) advertises its DP VDO as 0x405. This would
> fail
> the Pin Assignment compatibility check, despite it supporting
> Pin Assignment C as a UFP.
> 
> Update the check to use the correct DP Pin Assign macros that
> take the peripheral's receptacle bit into account.
> 
> Fixes: c1e5c2f0cb8a ("usb: typec: altmodes/displayport: correct pin
> assignment for UFP receptacles")
> Cc: stable@...r.kernel.org
> Reported-by: Diana Zigterman <dzigterman@...omium.org>
> Signed-off-by: Prashant Malani <pmalani@...omium.org>
> ---
> 
> I realize this is a bit late in the release cycle, but figured since
> it
> is a fix it might still be considered. Please let me know if it's too
> late and I can re-send this after the 6.3-rc1 is released. Thanks!


on the imx8mq-librem5r4.dts board, when using a typec-hub with HDMI,
this patch breaks image output in one case for me: For a monitor where
negotiation of resolution fails, a lower resolution works though, I now
get an oops and hence an unusable system, see the
dmesg_typec_hub_hdmi_new.txt logs I append. this should definitely not
happen.

with your patch reverted, I get no oops and a perfectly usable system
like before, which is the file dmesg_typec_hub_hdmi_old_ok.txt

could this patch be wrong or at least no universally good for everyone?
it looks like a regression to me.

thanks a lot!

                                  martin


View attachment "dmesg_typec_hub_hdmi_new.txt" of type "text/plain" (16594 bytes)

View attachment "dmesg_typec_hub_hdmi_old_ok.txt" of type "text/plain" (8353 bytes)