kernel docspdf compile failed

Background

Recently I am doing USB task and need and manual to know more usb frameworks in android 8.0.Then I try to compile the docspdf . Finally I failed to do that instead of mandocs.

process to make pdfdocs

$:cd kernel_path

$:sudo apt-get install python-sphinx texlive-xetex collection-fontsrecommended texlive-fonts-recommended

$:make pdfdocs

(/usr/share/texlive/texmf-dist/tex/latex/l3kernel/l3candidates.sty))
(/usr/share/texlive/texmf-dist/tex/latex/l3packages/xparse/xparse.sty)

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!
! Fatal fontspec error: "cannot-use-pdftex"
! 
! The fontspec package requires either XeTeX or LuaTeX to function.
! 
! You must change your typesetting engine to, e.g., "xelatex" or "lualatex"
! instead of plain "latex" or "pdflatex".
! 
! See the fontspec documentation for further information.
! 
! For immediate help type H .
!...............................................  
                                                  
l.41  }
       
 ) )
(see the transcript file for additional information)
No pages of output.

pdfTeX warning: pdflatex: dangling objects discarded, no output file produced.
Transcript written on development-process.log.
make[2]: *** [development-process.pdf] Error 1
make[1]: *** [pdfdocs] Error 2
make: *** [pdfdocs] Error 2

failed.

Then this link leads me to another way.

process to make mandocs

$:make mandocs

$:make install docs

scripts/kconfig/conf  --silentoldconfig Kconfig
.config:282:warning: override: reassigning to symbol USB_NET_DRIVERS
*
* Restart config...
*
*
* Linux/x86 4.9.56 Kernel Configuration
*
64-bit kernel (64BIT) [Y/n/?] (NEW) 

....

but still failed.