I don't know, if this question is off-topic for Stackoverflow, but before I ask this question in the official U-Boot mailing-list I will ask this on this site.
Have started a bare-metal application (simple Kernel) for the purpose of education. Now I want to implement a simple initrd support for loading Kernel modules and load and execute the user application.
Is it possible (maybe with workarounds) with U-Boot to pass multiple arguments in the AArch64 registers, when booting an ELF image?
I know it's maybe possible with the U-Boot bootm command. But I haven't currently figured out, how it fully works. The U-Boot documentation refers to the Linux documentation. According to this documentation only register x0 should be filled with the device-tree-blob address, which I haven't implemented at this time. x1, x2, x3 are reserved and should be filled with zeros:
Primary CPU general-purpose register settings:
x0 = physical address of device tree blob (dtb) in system RAM.
x1 = 0 (reserved for future use)
x2 = 0 (reserved for future use)
x3 = 0 (reserved for future use)
No idea where I can get the other arguments.
You have two options:
The booti command will add the start and end address to the device tree, e.g.
/ {
chosen {
linux,initrd-start = <0x82000000>;
linux,initrd-end = <0x82800000>;
};
};
Please, find the booti command description here:
https://u-boot.readthedocs.io/en/latest/usage/booti.html
The other possibility is booting via UEFI.
With the efidebug command you can define a boot option, e.g. Boot0000 indicating the location of the kernel and of the initrd. The initrd will be exposed as a EFI_LOAD_FILE2_PROTOCOL when you run 'bootefi bootmgr'.
Or from the EFI stub of your kernel you use the UEFI file protocol to load the initrd.
Building UEFI applications is the easiest using gnu-efi.
Besides the mailing list, there is an #u-boot IRC channel on Freenode.
There's a 3rd option, which is bootelf which looking at cmd/elf.c
/*
* pass address parameter as argv[0] (aka command name),
* and all remaining args
*/
rc = do_bootelf_exec((void *)addr, argc, argv)
Related
I am writing a bootloader for my Arm board (32-bit i.MX6) and want to boot the Linux kernel using a device tree and an initrd file located at a static location in memory.
I looked to U-Boot as a reference and I see I can use the bootm command to provide a kernel, device tree and ramdisk:
Boot application image from memory:
bootm [addr [arg ...]] - boot application image stored in memory passing arguments 'arg
...'; when booting a Linux kernel,‘arg' can be the address of an initrd image
I know there are two ways to pass information from a bootloader to the kernel, the legacy ATAGS method and the modern device tree method.
With ATAGS this can be achieved with the ATAG_INITRD2 tag which describes the address that a ramdisk is stored in memory. However, with a flattened device tree no ATAGS are passed to the kernel (which is shown in the boot log with the "No ATAGs?" message). I do not see any method to specify a ramdisk when using a device tree.
If I look at the documentation for booting the Linux kernel on Arm I see the following interface is specified:
- CPU register settings
r0 = 0,
r1 = machine type number discovered in (3) above.
r2 = physical address of tagged list in system RAM, or
physical address of device tree block (dtb) in system RAM
In fact, the same document states that an initramfs must be configured prior to booting, yet includes no details on how to do so when booting with a device tree.
Is there some alternative way to achieve this? Is the required information appended to the device tree automatically by U-Boot, or is there an alternative way to notify the kernel of the ramdisk location?
It will be patched in the dtree by the bootloader; e.g.
/ {
chosen {
linux,initrd-start = <0x....>;
linux,initrd-end = <0x....>;
};
Coming form this question yesterday, I decided to port this library to my board. I was aware that I needed to change something, so I compiled the library, call it on a small program and see what happens. The 1st problem is here:
// Check for GPIO and peripheral addresses from device tree.
// Adapted from code in the RPi.GPIO library at:
// http://sourceforge.net/p/raspberry-gpio-python/
FILE *fp = fopen("/proc/device-tree/soc/ranges", "rb");
if (fp == NULL) {
return MMIO_ERROR_OFFSET;
}
This lib is aimed for Rpi, os the structure of the system on my board is not the same. So I was wondering if somebody could tell me where I could find this file or how it looks like so I can find it by my self in order to proceed the job.
Thanks.
You don't necessarily want that "file" (or more precisely /proc node).
The code this is found in is setting up to do direct memory mapped I/O using what appears to be a pi-specific gpio-flavored version of the /dev/mem type of device driver for exposing hardware special function registers to userspace.
To port this to your board, you would need to first determine if there is a /dev/mem or similar capability in your kernel which you can activate. Then you would need to determine the appropriate I/O registers for GPIO pins. The pi-specific code is reading the Device Tree to figure this out, but there are other ways, for example you can manually read the programmer's manual of the SoC on which you are running.
Another approach you can consider is adding some small microcontroller (or yes, barebones ***duino) to the system, and using that to collect information from various sensors and peripherals. This can then be forwarded to the SoC over a UART link, or queried out via I2C or similar - add a small amount of cost and some degree of bottleneck, but also means that the software on the SoC then becomes very portable - to a different comparable chip, or perhaps even to run on a desktop PC during development.
I am trying to port drivers from old kernel to new one on ARM based platform. While porting one of the drivers I have noticed that request_irq fails on new kernel. Actually, what this driver have is a number of hard coded irq numbers, and it tries to request_irq for this HW lines. I started to search what is the reason of request_irq failure, - the reason is that the appropriate IRQ descriptor (irq_desc) have IRQ_NOREQUEST flag set.
I started to search where this flag is cleared, and found that it happens here:
of_platform_populate
|
...
|
of_device_alloc
|
...
|
irq_of_parse_and_map
(some levels below this flag is dropped)
So that code is invoked from mach init code and parse DTB, all interrupt numbers that are mentioned in DTB would be mapped to irq virtual space and will be accessible through appropriate devices structures, for example:
irq = platform_get_irq(pdev, 0);
As I already said, this old - fashion drivers just have hard-coded irq numbers in include files, and they don't have no appropriate dtb entries.
The question is what is the right way, from the kernel perspective of view, to port this? Do I need to make this old driver a platform device (now it is just a char device) and create appropriate dtb description for it? Or I can just use some kernel API to mark this interrupts as available? Is it a common/normal style?
I read that the Software generated interrupts in ARM are used as Inter-processor interrupts. I can also see that 5 of those interrupts are already in use. I also know that ARM provides 16 Software generated interrupts.
In my application i am running a bare metal application on of the ARM-cortex cores and Linux on the other. I want to communicate some data from the core running bare metal application to the core which is running Linux. I plan to copy the data to the on chip memory ( which is shared) and I will trigger a SGI on the Core ( running linux) to indicate some data is available for it to process. Now I am able to generate the SGI from the core ( running bare-metal application ). But for handling the interrupt in the linux side, I am not sure of the SGI IRQ numbers which are free and I am also not sure whether i can use the IRQ number directly ( in general SGI are from 0-15). Does any one have an idea how to write a handler for SGI in Linux?
Edit: This is a re-wording of the above text, because the question was closed for SSCE reasons. The Cortex-A CPUs are used in multi-CPU systems. An ARM generic interrupt controller (GIC) monitors all global interrupts and dispatches them to a particular CPU. In order for individual CPUs to signal each other, a software generated interrupt (SGI) is sent from one core to the other; this uses peripheral private interrupts (PPI). This question is,
How to implement a Linux kernel driver that can receive an SGI as a PPI?
Does any one have an idea how to write a handler for SGI in Linux?
As you didn't give the Linux version, I will assume you work with the latest (or at least recent). The ARM GIC has device tree bindings. Typically, you need to specify the SGI interrupt number in a device tree node,
ipc: ipc#address {
compatible = "company,board-ipc"; /* Your driver */
reg = <address range>;
interrupts = <1 SGI 0x02>; /* SGI is your CPU interrupt. */
status = "enabled";
};
The first number in the interrupt stanza denotes a PPI. The SGI will probably be between 0-15 as this is where the SGI interrupts are routed (at least on a Cortex-A5).
Then you can just use the platform_get_irq() in your driver to get the PPI (peripheral private interrupt). I guess that address is the shared memory (physical) where you wish to do the communications; maybe reg is not appropriate, but I think it will work. This area will be remapped by the Linux MMU and you can use it with,
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
mem = devm_ioremap_resource(dev, res);
The address in the device tree above is a hex value of the physical address. The platform_get_irq() should return an irq number which you can use with the request_irq() family of functions. Just connect this to your routine.
Edit: Unfortunately, interrupts below 16 are forbidden by the Linux irq-gic.c. For example, gic_handle_irq(), limits handler to interrupts between 16 and 1020. If SMP is enabled, then handle_IPI() is called for the interrupts of interest. gic_raise_softirq() can be used to signal an interrupt. To handle the SGI with the current Linux, smp.c needs additional enum ipi_msg_type values and code to handle these in handle_IPI(). It looks like newer kernels (3.14+ perhaps?) may add a set_ipi_handler() to smp.c to make such a modification unneeded.
I would like to add that an example of such inter-core communication can be found in TI multicore SoC's (i.e. OMAP3530). Some time ago when I was using such a mechanism, means were provided by TI. Specifically, it was the DSPLink Linux device driver which was providing such a functionality. At that time, unfortunately, it wasn't an open source solution, but maybe there is some technical paper from TI describing how it works ... Just a direction what you could investigate further :)
EDIT: In the meantime, it seems that they've made it open source. So, if that's what you are looking for, you can have a look: DSPLink and SysLink (successor of DSPLink)
While in u-boot of my ARM based board (DM368) I mark some kernel partition block manually as bad. U-boot says that it was marked and, for example, while writing/reading kernel image I see it skipping this bad block.
But when I try to write the same partition from within Linux (loaded via NFS) I see that Linux nandwrite command USES this bad block! I checked this in several ways - Linux ignores bad block mark for 100%. But everywhere in the internet it is said that BBT is one for both u-boot and Linux.
So, where is the catch?
OK, the answer is found.
For some unclear reason Texas Instruments, manufacturer of the board DM365EVM which I use for development, provides the kernel with different BBT structure. They defined BBT offset as 2, while all the world, including the provided u-boot, defines this offset as 8.
I wish them a good health for many years.