init_tis() takes 50 ms on Dell XPS 13 9360 – almost 10 % of whole time until initrd

[Paul Menzel]

Dear Linux folks,


Trying to optimize the boot time of Linux on the Dell XPS 13 9360, 
probing of MSFT0101:00 takes 52 ms, making `init_tis()` taking almost 10 
% alone until starting the initrd:

    [    0.000000] Linux version 6.8.0-rc4 
(build@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx) (gcc (Debian 13.2.0-13) 13.2.0, 
GNU ld (GNU Binutils for Debian) 2.42) #20 SMP PREEMPT_DYNAMIC Mon Feb 
12 09:40:49 CET 2024
    […]
    [    0.000000] DMI: Dell Inc. XPS 13 9360/0596KF, BIOS 2.21.0 
06/02/2022
    […]
    [    0.320057] calling  init_tis+0x0/0x100 @ 1
    [    0.332190] tpm_tis MSFT0101:00: 2.0 TPM (device-id 0xFE, rev-id 4)
    [    0.372164] probe of MSFT0101:00 returned 0 after 52101 usecs
    [    0.372186] initcall init_tis+0x0/0x100 returned 0 after 52127 usecs
    […]
    [    0.588643] Freeing unused decrypted memory: 2036K
    [    0.589068] Freeing unused kernel image (initmem) memory: 3976K
    [    0.606115] Write protecting the kernel read-only data: 22528k
    [    0.606527] Freeing unused kernel image (rodata/data gap) 
memory: 276K
    [    0.652327] x86/mm: Checked W+X mappings: passed, no W+X pages 
found.
    [    0.652329] x86/mm: Checking user space page tables
    [    0.695968] x86/mm: Checked W+X mappings: passed, no W+X pages 
found.
    [    0.696104] Run /init as init process
    […]

For users, where boot time is most important, can this be moved out of 
the hot path somehow?


Kind regards,

Paul