Pass large amount of binary data from u-boot to linux kernel

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You could use a custom ATAG to either pass the data block or to pass the address & length of the data. Note that the “A” in ATAG stands for ARM, so this solution is not portable to other architectures. An ATAG is preferable to a command-line bootarg IMO because you do not want the user to muck with physical memory addresses. Also the Linux kernel will process the ATAG list before the MMU (i.e. virtual memory) is enabled.

In U-Boot, look at lib_arm/armlinux.c or arch/arm/lib/bootm.c for routines that build the ARM tag list. Write your own routine for your new tag(s), and then invoke it in do_bootm_linux().

In the Linux kernel ATAGs are processed in arch/arm/kernel/setup.c, when virtual memory has not yet been enabled. If you just pass an address & length values from U-Boot, then the pointer & length can be assigned to global variables that are exported, 

void          *my_data;
unsigned int  my_dlen;
EXPORT_SYMBOL(my_data);
EXPORT_SYMBOL(my_dlen);

and then the driver can retrieve it.

extern void          *my_data;
extern unsigned int  my_dlen;

request_mem_region(my_data, my_dlen, DRV_NAME);
md_map = ioremap(my_data, my_dlen);

I’ve used similar code to probe for SRAM in U-Boot, then pass the starting address & number of KBytes found to the kernel in a custom ATAG. A kernel driver obtains these values, and if they are nonzero and have sane values, creates a block device out of the SRAM. The major difference from your situation is that the SRAM is in a completely different physical address range from the SDRAM.

NOTE
An ATAG is built by U-Boot for the physical memory that the kernel can use, so this is really where you need to define and exclude your reserved RAM. It’s probably too late to do that in the kernel.

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