On 2/14/23 23:58, Mika Westerberg wrote:
Hi,
On Tue, Feb 14, 2023 at 09:46:45AM -0600, Mario Limonciello wrote:
Some TBT3 devices have a hard time reliably responding to bit banging
requests correctly when connected to AMD USB4 hosts running Linux.
These problems are not reported in any other CM, and comparing the
implementations the Linux CM is the only one that utilizes bit banging
to access the DROM. Other CM implementations access the DROM directly
from the NVM instead of bit banging.
I'm sure Apple CM uses bitbanging because it is what Andreas reverse
engineered when he added the initial Linux Thunderbolt support ;-) I
guess this is then only Window CM? The problem with reading NVM directly
is that we may lose things like UUID, so I'm wondering if there is
something else going on.
When I say other CMs, maybe I should have specified which ones were
checked :)
The following CM get the DROM without bit-banging:
Win11 CM (MS inbox)
Win10 CM (AMD)
Pre-OS CM (AMD)
Can you give some details, like what is the device in question?
It happens with both AR and TR based TBT3 devices connected to AMD USB4
router.
It's not any one specific vendor or model, we've seen it across multiple
vendors with
a failure rate of about 30%.
With an analyzer connected in between we can see that the connected TBT3
device
does respond to the bit banging correctly, but the response is not
making it over to
the USB4 router.
It happens with multiple retimer vendors, but it hasn't been checked on
a retimer-less
system yet.
Adjust the flow to try this on TBT3 devices before resorting to bit
banging.
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
drivers/thunderbolt/eeprom.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/thunderbolt/eeprom.c b/drivers/thunderbolt/eeprom.c
index c90d22f56d4e1..d9d9567bb938b 100644
--- a/drivers/thunderbolt/eeprom.c
+++ b/drivers/thunderbolt/eeprom.c
@@ -640,6 +640,10 @@ int tb_drom_read(struct tb_switch *sw)
return 0;
}
+ /* TBT3 devices have the DROM as part of NVM */
+ if (tb_drom_copy_nvm(sw, &size) == 0)
+ goto parse;
+
res = tb_drom_read_n(sw, 14, (u8 *) &size, 2);
if (res)
return res;
--
2.25.1
I guess something else that might be less detrimental the loss of UUID
by reading DROM this way would be to only read DROM this way if any CRC
failed.
