[coreboot] [RFC] MMC support in coreboot

[mrnuke]

On 01/10/2014 12:39 PM, Kevin O'Connor wrote:
> On Thu, Jan 09, 2014 at 01:46:19AM -0600, mrnuke wrote:
>> It's essential for some ARM SoCs. Allwinner chips like the MMC as their
>> first boot source, and people are very happy with having their firmware
>> and linux on micro SD. It makes the system unbrickable.
> 
> Can you expand on this requirement?  Do these machines have a regular
> flash/rom with code that reads the rest of the firmware from the block
> device, or is some portion of the block device mapped by hardware at
> startup and that portion is tasked with reading the rest of the
> firmware off the block device?  If so, how big is the initial mapped
> area?
> 

A blob built-in the SoC reads in some of the firmware (from SD, MMC or
SPI, load to SRAM @ 0x0, branch to 0x0). 24 KiB on A10, a little
different on A13 and so on. Think of it as the coreboot bootblock.
That's all the free ride that you get. romstage and others you have to
load manually.