linux-kernel - Re: [PATCH v4 0/3] Fix problems fetching TBT3 DROM from AMD USB4 routers

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Date:   Mon, 6 Mar 2023 11:57:53 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     linux-usb@...r.kernel.org, Sanju.Mehta@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/3] Fix problems fetching TBT3 DROM from AMD USB4
 routers

Hi Mario,

On Thu, Feb 23, 2023 at 03:07:40PM -0600, Mario Limonciello wrote:
> 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 when devices have an LC.
> 
> v4:
>  * Style fixups
>  * Fixup for wrong path for USB4 devices
> 
> Mario Limonciello (3):
>   thunderbolt: Adjust how NVM reading works
>   thunderbolt: use `tb_eeprom_get_drom_offset` to discover DROM offset
>   thunderbolt: Refactor DROM reading

I split the device side into a separate function too, renamed root
switch to host router (as that's the correct USB4 term), and fixed a
couple style issues and applied to thunderbolt.git/next, thanks!

Please check that I did not mess up anything :)