Re: Question about xen and Rasp 4B

[Jukka Kaartinen <jukka.kaartinen@xxxxxxxxxx>]

On 4.2.2021 0.12, Elliott Mitchell wrote:
> 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...).
Without the overlay GPU driver (v3d) was not probed. And you need to use 
the fakekms.