Hi RD,

On Mon, Oct 16, 2023 at 3:56 PM RD Babiera rdbabiera@google.com 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.

Fixes: 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode") Cc: stable@vger.kernel.org Signed-off-by: RD Babiera rdbabiera@google.com

---

drivers/usb/typec/altmodes/displayport.c | 9 +++++++++ 1 file changed, 9 insertions(+)

diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c index 718da02036d8..3b35a6b8cb72 100644 --- a/drivers/usb/typec/altmodes/displayport.c +++ b/drivers/usb/typec/altmodes/displayport.c @@ -575,9 +575,18 @@ int dp_altmode_probe(struct typec_altmode *alt) struct fwnode_handle *fwnode; struct dp_altmode *dp; int ret;

•   int port_cap, partner_cap;
  

VDOs are 32-bit, so u32 is probably better here.

    /* FIXME: Port can only be DFP_U. */

•   /* Make sure that the port and partner can resolve into source and sink */
  

•   port_cap = DP_CAP_CAPABILITY(port->vdo);
  

•   partner_cap = DP_CAP_CAPABILITY(alt->vdo);
  

•   if (!((port_cap & DP_CAP_DFP_D) && (partner_cap & DP_CAP_UFP_D)) &&
  

nit: bitwise '&' has a higher precedence than logical '&&', so the innermost parentheses shouldn't be necessary:

if (!(port_cap & DP_CAP_DFP_D && partner_cap & DP_CAP_UFP_D) && !(port_cap & DP_CAP_UFP_D && partner_cap & DP_CAP_DFP_D)) return -ENODEV; ...

OTOH, perhaps you should just introduce a macro that performs this bitwise operation for even better readability. Something like

#define DP_CAP_IS_DFP_D(_cap_) (!!(DP_CAP_CAPABILITY(_cap_) & DP_CAP_DFP_D))

(not sure if "!!" is tolerated in kernel style, but you get the gist...)

•       !((port_cap & DP_CAP_UFP_D) && (partner_cap & DP_CAP_DFP_D))) {
  

•           return -ENODEV;
  

Single line if statements can drop curly braces [1]

Best regards,

-Prashant

[1] https://www.kernel.org/doc/html/v4.10/process/coding-style.html#placing-brac...