linux-kernel - [PATCH v2 0/2] Fix problems fetching TBT3 DROM from AMD USB4 routers

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Message-ID: <20230215172520.8925-1-mario.limonciello@amd.com>
Date:   Wed, 15 Feb 2023 11:25:18 -0600
From:   Mario Limonciello <mario.limonciello@....com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        <linux-usb@...r.kernel.org>
CC:     <Sanju.Mehta@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 0/2] Fix problems fetching TBT3 DROM from AMD USB4 routers

TBT3 devices when connected to an AMD USB4 router occasionally fail to
properly respond to requests for the DROM via bit banging.

Depending upon which part of the request failed will impact the severity.
A number of workarounds have been put in place to let the driver handle
the failed requests:

commit e87491a9fd4e3 ("thunderbolt: Retry DROM reads for more failure scenarios")
commit a283de3ec646f ("thunderbolt: Do not resume routers if UID is not set")
commit 6915812bbd109 ("thunderbolt: Do not make DROM read success compulsory")
commit f022ff7bf377 ("thunderbolt: Retry DROM read once if parsing fails")

Still even with these changes the failures do make it through. In comparing
other CM implementations utilized on AMD systems, they all access the
DROM directly from the NVM.

To avoid triggering this issue, try to get the DROM directly from the NVM
in Linux as well before resorting to bitbanging.

Mario Limonciello (2):
  thunderbolt: Adjust how NVM reading works
  thunderbolt: use `tb_eeprom_get_drom_offset` to discover DROM offset

 drivers/thunderbolt/eeprom.c | 150 +++++++++++++++++++----------------
 1 file changed, 82 insertions(+), 68 deletions(-)

-- 
2.34.1