linux-kernel - Re: [PATCH v2] usb: typec: altmodes/displayport: verify compatible source/sink role combination

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Date:   Thu, 19 Oct 2023 11:19:44 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     RD Babiera <rdbabiera@...gle.com>
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, badhri@...gle.com,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] usb: typec: altmodes/displayport: verify compatible
 source/sink role combination

On Wed, Oct 18, 2023 at 08:34:09PM +0000, RD Babiera wrote:
> DisplayPort Alt Mode CTS test 10.3.8 states that both sides of the
> connection shall be compatible with one another such that the connection
> is not Source to Source or Sink to Sink.
> 
> The DisplayPort driver currently checks for a compatible pin configuration
> that resolves into a source and sink combination. The CTS test is designed
> to send a Discover Modes message that has a compatible pin configuration
> but advertises the same port capability as the device; the current check
> fails this.
> 
> Verify that the port and port partner resolve into a valid source and sink
> combination before checking for a compatible pin configuration.
> 
> ---
> Changes since v1:
> * Fixed styling errors
> * Added DP_CAP_IS_UFP_D and DP_CAP_IS_DFP_D as macros to typec_dp.h
> ---
> 
> Fixes: 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode")
> Cc: stable@...r.kernel.org
> Signed-off-by: RD Babiera <rdbabiera@...gle.com>

Acked-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>

> ---
>  drivers/usb/typec/altmodes/displayport.c | 5 +++++
>  include/linux/usb/typec_dp.h             | 2 ++
>  2 files changed, 7 insertions(+)
> 
> diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
> index 718da02036d8..9c17955da570 100644
> --- a/drivers/usb/typec/altmodes/displayport.c
> +++ b/drivers/usb/typec/altmodes/displayport.c
> @@ -578,6 +578,11 @@ int dp_altmode_probe(struct typec_altmode *alt)
>  
>  	/* FIXME: Port can only be DFP_U. */
>  
> +	/* Make sure that the port and partner can resolve into source and sink */
> +	if (!(DP_CAP_IS_DFP_D(port->vdo) && DP_CAP_IS_UFP_D(alt->vdo)) &&
> +	    !(DP_CAP_IS_UFP_D(port->vdo) && DP_CAP_IS_DFP_D(alt->vdo)))
> +		return -ENODEV;
> +
>  	/* Make sure we have compatiple pin configurations */
>  	if (!(DP_CAP_PIN_ASSIGN_DFP_D(port->vdo) &
>  	      DP_CAP_PIN_ASSIGN_UFP_D(alt->vdo)) &&
> diff --git a/include/linux/usb/typec_dp.h b/include/linux/usb/typec_dp.h
> index 1f358098522d..4e6c0479307f 100644
> --- a/include/linux/usb/typec_dp.h
> +++ b/include/linux/usb/typec_dp.h
> @@ -67,6 +67,8 @@ enum {
>  #define   DP_CAP_UFP_D			1
>  #define   DP_CAP_DFP_D			2
>  #define   DP_CAP_DFP_D_AND_UFP_D	3
> +#define DP_CAP_IS_UFP_D(_cap_)		(!!(DP_CAP_CAPABILITY(_cap_) & DP_CAP_UFP_D))
> +#define DP_CAP_IS_DFP_D(_cap_)		(!!(DP_CAP_CAPABILITY(_cap_) & DP_CAP_DFP_D))
>  #define DP_CAP_DP_SIGNALLING(_cap_)	(((_cap_) & GENMASK(5, 2)) >> 2)
>  #define   DP_CAP_SIGNALLING_HBR3	1
>  #define   DP_CAP_SIGNALLING_UHBR10	2
> 
> base-commit: 5220d8b04a840fa09434072c866d032b163419e3
> -- 
> 2.42.0.655.g421f12c284-goog

-- 
heikki