Re: [U-Boot] [PATCH 1/2] Pass through start.elf bootargs on Raspberry Pi

On 11/29/2015 11:40 AM, Marco Schuster wrote:

On Raspberry Pi, the primary bootloader start.elf uses the options in config.txt, as well as options hidden in the firmware itself, to tell the Linux kernel e.g. framebuffer sizes, memory regions, MAC addresses and more.

Was this patch sent using "git send-email"? I assume not, since it is corrupted due to wrapping.

I suspect ./scripts/checkpatch.pl also wasn't run, since it would complain about over-long lines, and multiple other formatting errors.

Normally, u-boot would not be able to pass through these options to the Linux kernel. This patch adds pass-through support via an additional env variable "bootargs_orig" which is loaded with the original cmdline obtained from ATAG or the FDT.

In addition, this allows the user to configure DT overlays the "Pi way" by enabling them in config.txt, as this patch passes through the full FDT if it has been passed one by u-boot.

Note that, as stated in the comment block, for FDT passthrough to work, the u-boot.img must be run through a perl script by the Raspberry Pi Foundation, which appends a trailer to the image telling start.elf to supply a FDT instead of an ATAG struct.

This feature sounds fine. However, it should be optional. It likely only makes sense when booting a downstream Pi Foundation kernel, and not when booting an upstream/mainline kernel with matching DT using the standardized DT bindings. As such, I think this feature should be optional (e.g. perhaps en-/dis-abled by an environment variable at run-time) so that the user gets to choose whether to use the feature.

diff --git a/board/raspberrypi/rpi/rpi.c b/board/raspberrypi/rpi/rpi.c index 6451d1d..d8d0fbb 100644 --- a/board/raspberrypi/rpi/rpi.c +++ b/board/raspberrypi/rpi/rpi.c @@ -259,6 +259,72 @@ int misc_init_r(void) #ifdef CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG set_board_info(); #endif

•   /*
  

•    * The RPi start.elf passes important system configuration
  

•    * like memory sizes and LED GPIO assignments to the kernel
  

•    * via kernel command line.
  

•    *
  

•    * Therefore we have to parse the passed ATAG or FDT to get the
  

s/have to/may/

•    * commandline and pass it through to script-land via the env
  

•    * variable "bootargs_orig" so it can be passed on.
  

•    *
  

•    * By default, start.elf assumes a non-DT capable kernel and
  

•    * passes the commandline via ATAG; this requires u-boot to
  

•    * load the FDT from /boot and pass it on. This works if no
  

•    * overlays have been passed through, but once overlays are in
  

•    * the mix, stuff gets complicated to do in u-boot.
  

Ideally, DT overlays would be either implemented in U-Boot, or deferred until the kernel boots and user-space can load overlays. I suspect the latter is more inline with the usage model expected by upstream/mainline, although I haven't checked to see.

•    *
  

•    * To force start.elf to pass a processed, ready-to-go DT,
  

•    * you have to use the mkknlimg tool on the u-boot image:
  

•    * ./mkknlimg --dtok u-boot.bin /boot/u-boot.bin
  

•    *
  

•    * mkknlimg can be obtained from
  

https://github.com/raspberrypi/tools/blob/master/mkimage/knlinfo

•    *
  

•    * User scripts can check for successful bootargs retrieval
  

•    * in the env variable pi_bootmode, which is either fdt, atag
  

•    * or unknown in case of an error.
  

•    *
  

•    * The location 0x100 is hard-coded in start.elf, and it is
  

•    * the same as in the default bootscripts, so you only have
  

•    * to omit the fatload command loading the raw FDT to get
  

•    * going.
  

"omit the fatload command" from where?

Personally I've been using extlinux.conf on my Pi for a while, so there is no "fatload" anywhere that I'm aware of.

•    */
  

•   void* ptr = (char*) 0x100;
  

•   struct tag_header* atag_ptr = ptr;
  

•   setenv("pi_bootmode","unknown");
  

•   if(atag_ptr->tag != ATAG_CORE) {
  

•           if(atag_ptr->size == be32_to_cpu(FDT_MAGIC)) {
  

•                   set_working_fdt_addr((ulong) ptr);
  

Doesn't that set the address of the DT that U-Boot uses to configure itself, not the DT that U-Boot will pass to the kernel? The two are certainly separate concepts. This code should set $fdt_addr/$fdt_addr_r if the DT is detected, so that scripts can affect whether this DT is used.

•                   int nodeoffset = fdt_path_offset(working_fdt,
  

"/chosen");

•                   int len;
  

•                   const void* nodep = fdt_getprop(working_fdt,
  

nodeoffset, "bootargs", &len);

•                   if(len==0) {
  

•                           printf("WARNING: Could not determine
  

bootargs from FDT!\n");

•                   } else {
  

•                           printf("Set bootargs_orig from FDT\n");
  

debug() seems more appropriate than printf(), except for errors.

•                           setenv("bootargs_orig", (char*) nodep);
  

•                           setenv("pi_bootmode","fdt");
  

•                   }
  

•           } else {
  

•                   printf("Warning: start.elf did not pass ATAG
  

or FDT parameters\n");

•           }
  

•   } else {
  

•           while(atag_ptr->tag != ATAG_NONE) {
  

•                   printf("at %p, have %x (len
  

%x)\n",atag_ptr,atag_ptr->tag, atag_ptr->size);

•                   if(atag_ptr->tag == ATAG_CMDLINE) {
  

•                           char* old_cmdline = ptr + 8;
  

•                           printf("Set bootargs_orig from ATAG\n");
  

•                           setenv("bootargs_orig", old_cmdline);
  

•                           setenv("pi_bootmode", "atag");
  

•                   }
  

•                   ptr = ptr + (atag_ptr->size * 4);
  

•                   atag_ptr=ptr;
  

•           }
  

•   }
  

•   return 0;
  

}