Re: netbsd-9, boot, EFI and device tree

[tlaronde%polynum.com@localhost]

On Sun, Apr 25, 2021 at 06:42:19PM +0200, Manuel Bouyer wrote:
> On Sun, Apr 25, 2021 at 12:31:40PM +0200, tlaronde%polynum.com@localhost wrote:
> > On Fri, Apr 23, 2021 at 10:02:37PM +0200, Manuel Bouyer wrote:
> > > Hello,
> > > I'm starting a new project with an Olimex A20 lime2 board.
> > > Up to now I used the old way of loading the kenrel from u-boot, where I can
> > > also pass kernel command line and device tree blobs.
> > > I though that for this new projet I would start with a fresh install,
> > > and so with EFI. But I didn't find much informations about it.
> > > 
> > > What is the way to load a specific device tree, and set some kernel
> > > boot options ?
> > 
> > From documentation and experiments, the problem is that the BROM on the
> > Sunxi SoC (hence the olimex-a20-olinuxino) does not provide an UEFI
> > environment, neither a SPL (Second Program Loader) nor a shell.
> > 
> > The BROM checks for uboot in some locations, in this case on the uSD.
> > 
> > So one needs to install U-Boot in every case.
> > 
> > Then U-Boot will act as specified by UEFI, looking in all devices for a 
> > FAT partition, looking for a /EFI/BOOT/ directory and, in this
> > directory, a EFI program with a standardized name.
> > 
> > In this case this is bootarm.efi, that is compiled during the building
> > of the NetBSD release.
> > 
> > De facto, if U-Boot has been compiled with the DTS, the only file needed
> > is the UEFI second stage bootloader (bootarm.efi for an arm32) and
> > that's all.
> > 
> > So the process is:
> > 
> > BROM (Sunxi SoC) -> SPL (U-Boot) 
> > 	-> (FAT partition)/EFI/BOOT/bootarm.efi (provided by NetBSD)
> > 	-> ('a' partition in NetBSD wedge): /netbsd
> > 
> > Even if it was possible (it is in theory possible) to bypass
> > bootarm.efi, letting U-Boot (providing UEFI) directly load an EFI aware
> > NetBSD kernel (but it doesn't seem at the moment possible from a
> > cursory look), U-Boot is mandatory for this SoC (I don't know if the
> > emmc version provides more UEFI i.e. has already U-Boot on it).
> > 
> > If I'm not mistaken, the "old" way was to provide an U-Boot version of
> > the kernel (the *.ub). It is not anymore required, since the EFI second
> > stage loader (bootarm.efi) can load the kernel.
> > 
> > In fact, I have tested with only U-Boot installed and
> > /EFI/BOOT/bootarm.efi on the FAT partition of the uSD card, and it
> > boots without ado.
> 
> Yes, that's how it works.
> 
> My problem is that I need a custom device tree (activate SPI2, more
> devices on I2C2, and so on). For this I found that there is a
> fdtfile variable in u-boot, that contains a dts file name which will
> be loaded from /dts/ on the FAT. So this part is solved.
> 
> The second issue (but not for this project) is that I need some
> kernel command line parameters (console=xxx, root=yyy for example).
> With u-boot loading netbsd.ub, I can set this in an u-boot variable.
> But I don't know how to do this with the EFI second-stage boot loader.
> 

Isn't boot.cmd in the root of the FAT partition (mounted as /boot)
for this?

From ${NETBSD_SRC_DIR}/distrib/utils/embedded/conf/armv7.conf
it seems to be used for this. The default file is
${NETBSD_SRC_DIR}/distrib/utils/embedded/files/armv7_boot.cmd
. But what is the set of commands and variables?


FWIW,
-- 
        Thierry Laronde <tlaronde +AT+ polynum +dot+ com>
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                    http://kertex.kergis.com/
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