Re: [PATCH RFC] thunderbolt: Skip reading Rsvd SB registers on older-gen hardware

[Greg Kroah-Hartman]

On Mon, Apr 13, 2026 at 12:54:41PM +0200, Konrad Dybcio wrote:
> From: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
> 
> The Linux TBT subsystem supports hardware aligned with the latest
> USB4 v2.0 specification. In some places though, it assumes registers
> only defined in that specification version (previously marked as
> Reserved) are always accessible.
> 
> Every version of the spec states:
> 
> """
> Unless specified otherwise, the Connection Manager shall not write a
> register with a value that is marked as “Rsvd”. Writing a register with
> a value that is marked as “Rsvd” results in undefined behavior.
> """
> 
> The effective list of SB registers that need this guarding currently
> exclusively contains ones that aren't used outside the debugfs dump
> logic, so just add the required checks there.
> 
> Fixes: 54e418106c76 ("thunderbolt: Add debugfs interface")
> Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
> ---
>  drivers/thunderbolt/debugfs.c | 20 ++++++++++++--------
>  drivers/thunderbolt/retimer.c | 11 ++++++++++-
>  drivers/thunderbolt/sb_regs.h | 11 ++++++-----
>  drivers/thunderbolt/tb.h      |  2 ++
>  4 files changed, 30 insertions(+), 14 deletions(-)
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
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- You have marked a patch with a "Fixes:" tag for a commit that is in an
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  Documentation/process/stable-kernel-rules.rst file for how to resolve
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thanks,

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