[PATCH] thunderbolt: Retry DROM read once if parsing fails

[Mika Westerberg <mika.westerberg@linux.intel.com>]

Kai-Heng reported that sometimes DROM parsing of ASUS PA27AC Thunderbolt 3
monitor fails. This makes the driver to fail to add the device so only
DisplayPort tunneling is functional.

It is not clear what exactly happens but waiting for 100 ms and retrying
the read seems to work this around so we do that here.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=206493
Reported-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Tested-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
 drivers/thunderbolt/eeprom.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/thunderbolt/eeprom.c b/drivers/thunderbolt/eeprom.c
index 3ebca44ab3fa..0c8471be3e32 100644
--- a/drivers/thunderbolt/eeprom.c
+++ b/drivers/thunderbolt/eeprom.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/crc32.h>
+#include <linux/delay.h>
 #include <linux/property.h>
 #include <linux/slab.h>
 #include "tb.h"
@@ -389,8 +390,8 @@ static int tb_drom_parse_entries(struct tb_switch *sw)
 		struct tb_drom_entry_header *entry = (void *) (sw->drom + pos);
 		if (pos + 1 == drom_size || pos + entry->len > drom_size
 				|| !entry->len) {
-			tb_sw_warn(sw, "drom buffer overrun, aborting\n");
-			return -EIO;
+			tb_sw_warn(sw, "DROM buffer overrun\n");
+			return -EILSEQ;
 		}
 
 		switch (entry->type) {
@@ -526,7 +527,8 @@ int tb_drom_read(struct tb_switch *sw)
 	u16 size;
 	u32 crc;
 	struct tb_drom_header *header;
-	int res;
+	int res, retries = 1;
+
 	if (sw->drom)
 		return 0;
 
@@ -612,7 +614,17 @@ int tb_drom_read(struct tb_switch *sw)
 		tb_sw_warn(sw, "drom device_rom_revision %#x unknown\n",
 			header->device_rom_revision);
 
-	return tb_drom_parse_entries(sw);
+	res = tb_drom_parse_entries(sw);
+	/* If the DROM parsing fails, wait a moment and retry once */
+	if (res == -EILSEQ && retries--) {
+		tb_sw_warn(sw, "parsing DROM failed, retrying\n");
+		msleep(100);
+		res = tb_drom_read_n(sw, 0, sw->drom, size);
+		if (!res)
+			goto parse;
+	}
+
+	return res;
 err:
 	kfree(sw->drom);
 	sw->drom = NULL;
-- 
2.28.0