Re: Question about xen and Rasp 4B

[Elliott Mitchell <ehem+xen@xxxxxxx>]

On Wed, Feb 03, 2021 at 12:55:40PM -0800, Stefano Stabellini wrote:
> On Wed, 3 Feb 2021, Jukka Kaartinen wrote:
> > On 3.2.2021 2.18, Stefano Stabellini wrote:
> > > How are you configuring and installing the kernel?
> > > 
> > > make bcm2711_defconfig
> > > make Image.gz
> > > make modules_install
> > > 
> > > ?
> > > 
> > > The device tree is the one from the rpi-5.9.y build? How are you loading
> > > the kernel and device tree with uboot? Do you have any interesting
> > > changes to config.txt?
> > > 
> > > I am asking because I cannot get to the point of reproducing what you
> > > are seeing: I can boot my rpi-5.9.y kernel on recent Xen but I cannot
> > > get any graphics output on my screen. (The serial works.) I am using the
> > > default Ubuntu Desktop rpi-install target as rootfs and uboot master.
> > > 
> > 
> > This is what I do:
> > 
> > make bcm2711_defconfig
> > cat "xen_additions" >> .config
> > make Image  modules dtbs
> > 
> > make INSTALL_MOD_PATH=rootfs modules_install
> > depmod -a
> > 
> > cp arch/arm64/boot/dts/broadcom/bcm2711-rpi-4-b.dtb boot/
> > cp arch/arm64/boot/dts/overlays/*.dtbo boot/overlays/
> 
> Thanks for the detailed instructions. This helps a lot. I saw below in
> boot2.source that you are using ${fdt_addr} as DTB source (instead of
> loading one), which means you are using the DTB as provided by U-Boot at
> runtime, instead of loading your own file.
> 
> With these two copies, I take you meant to update the first partition on
> the SD card, the one where config.txt lives, right? So that Xen is
> getting the DTB and overlays from the rpi-5.9.y kernel tree but passed
> down by the RPi loader and U-Boot?
> 
> I think the DTB must be the issue as I wasn't applying any overlays
> before. I ran a test to use the DTB and overlay from U-Boot but maybe I
> haven't updated them properly because I still don't see any output.

Seeing no graphics output from U-Boot is okay.  If the device-tree files
get sufficiently updated you can end up with no output from U-Boot, but
will get output once the Linux kernel's driver is operational (I've seen
this occur).

The most important part is having a HDMI display plugged in during the
early boot stages.  Unless the bootloader sees the display the output
won't get initialized and the Linux driver doesn't handle that.


> > dtoverlay=vc4-fkms-v3d,cma-64

This is odd.  My understanding is this is appropriate for RP3, but not
RP4.  For RP4 you can have "dtoverlay=disable-vc4" and still get graphics
output (hmm, I'm starting to think I need to double-check this...).


-- 
(\___(\___(\______          --=> 8-) EHM <=--          ______/)___/)___/)
 \BS (    |         ehem+sigmsg@xxxxxxx  PGP 87145445         |    )   /
  \_CS\   |  _____  -O #include <stddisclaimer.h> O-   _____  |   /  _/
8A19\___\_|_/58D2 7E3D DDF4 7BA6 <-PGP-> 41D1 B375 37D0 8714\_|_/___/5445