[net-next PATCH 3/6] net: phylink: Correctly handle PCS probe defer from PCS provider

[Christian Marangi <ansuelsmth@gmail.com>]

On using OF PCS implementation, it can happen that the PCS driver still
needs to be probed at the time the MAC driver calls .mac_select_pcs.

In such case, PCS provider will return probe defer as the PCS can't be
found in the global provider list. It's expected the MAC driver to
retry probing at a later time when the PCS driver is actually probed.

To handle this, check the return value of phylink_validate (that will
call mac_select_pcs to validate the interface) in phylink_create and
make phylink_create return -EPROBE_DEFER. The MAC driver will check this
return value and retry probing.

PCS can be removed unexpectedly at later time (driver gets removed) and
not available anymore. In such case, PCS provider will also return probe
defer as the PCS can't be found in the global provider list. (as the PCS
driver on removal will delete itself as PCS provider)

To communicate correct error message, in phylink_major_config() detect
this condition and treat -EPROBE_DEFER error from .mac_select_pcs as
-ENOENT as probe defer is only allowed at probe stage.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
---
 drivers/net/phy/phylink.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 7f71547e89fe..c6d9e4efed13 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -1395,6 +1395,15 @@ static void phylink_major_config(struct phylink *pl, bool restart,
 	if (pl->mac_ops->mac_select_pcs) {
 		pcs = pl->mac_ops->mac_select_pcs(pl->config, state->interface);
 		if (IS_ERR(pcs)) {
+			/* PCS can be removed unexpectedly and not available
+			 * anymore.
+			 * PCS provider will return probe defer as the PCS
+			 * can't be found in the global provider list.
+			 * In such case, return -ENOENT as a more symbolic name
+			 * for the error message.
+			 */
+			if (PTR_ERR(pcs) == -EPROBE_DEFER)
+				pcs = ERR_PTR(-ENOENT);
 			phylink_err(pl,
 				    "mac_select_pcs unexpectedly failed: %pe\n",
 				    pcs);
@@ -2004,7 +2013,18 @@ struct phylink *phylink_create(struct phylink_config *config,
 
 	linkmode_fill(pl->supported);
 	linkmode_copy(pl->link_config.advertising, pl->supported);
-	phylink_validate(pl, pl->supported, &pl->link_config);
+	ret = phylink_validate(pl, pl->supported, &pl->link_config);
+	/* The PCS might not available at the time phylink_create
+	 * is called. Check this and communicate to the MAC driver
+	 * that probe should be retried later.
+	 *
+	 * Notice that this can only happen in probe stage and PCS
+	 * is expected to be avaialble in phylink_major_config.
+	 */
+	if (ret == -EPROBE_DEFER) {
+		kfree(pl);
+		return ERR_PTR(ret);
+	}
 
 	ret = phylink_parse_mode(pl, fwnode);
 	if (ret < 0) {
-- 
2.48.1