Re: [REGRESSION][BISECTED] tpm: Popping noise in USB headphones since 1b6d7f9eb150

["Jarkko Sakkinen" <jarkko@kernel.org>]

Yeah, this is on the list.

See: https://bugzilla.kernel.org/show_bug.cgi?id=219383#c5

I had a fix for the AMD boot-time issue already over a month ago
but unfortunately took time to get enough feedback.

BR, Jarkko

On Fri Oct 25, 2024 at 3:11 AM EEST, Christian Heusel wrote:
> Hello everyone,
>
> Adam reports that since switching to the 6.10 kernel they have a popping
> sound from time to time (roughly every 10 minues) on their headphones
> which are connected via a [UGREEN's 5-in-1 USB-C Hub][0].
>
> We have then done a [lengthy bisection][1] on the mainline kernel which
> came to the conclusion that the following commit is the culprit of the
> issue:
>
>     1b6d7f9eb150 ("tpm: add session encryption protection to tpm2_get_random()")
>
> Since I thought that these results are likely not correct Adam has
> verified our results again by re-testing the bisection steps and again
> came to the same conclusion. Additionally I have shot the same question
> [at Jarkko on Mastodon] to find out if it's possible that changes in the
> TPM subsystem can have such an effect.. Without knowing the exact commit
> we had bisected to he pointed to the same functionality:
>
> > Jarkko Sakkinen (@jarkko@social.kernel.org):
> >
> > @gromit i might actually might have hunch for this but have been
> > unmotivated to move forward before these patches are merged. One thing
> > at a time IMHO, especially with performance fixes.
> > NOTE: this is a hyphothesis.
> >
> > tpm2_get_random() needs to be reconsidered with encryption as hwrng
> > calls it often enough and there's now more overhead.
> >
> > It pulls entropy in small chunks subtracting the length in the look
> > like you would use read() syscall from user space. This is not right.
> > This leads to small and variable size exchanges and yeah generally
> > that equates to an inefficient implemenation with bad latency
> > properties.
>
> If there are any patches to test or if further input is needed from the
> initial reporter on our Bugtracker we can do that!
>
> Thank you all for your hard work on the kernel!
>
> Cheers,
> Chris
>
>
> [0]: https://uk.ugreen.com/collections/hubs-1/products/ugreen-5-in-1-4k-hdmi-usb-c-hub
> [1]: https://gitlab.archlinux.org/archlinux/packaging/packages/linux/-/issues/79#note_210599
> [2]: https://chaos.social/@gromit/113345582873908273
>
> ---
> #regzbot introduced: 1b6d7f9eb150 
> #regzbot link: https://gitlab.archlinux.org/archlinux/packaging/packages/linux/-/issues/79
> #regzbot link: https://chaos.social/@gromit/113345582873908273
> #regzbot title: tpm: popping sound in headphones connected via USB-C