fel: add FEL protocol and soc_info_t struct documentation#241
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Add a markdown document describing the basics of the FEL protocol, to give some idea about the expectations and limitations of the protocol. Also add a description for each member of the soc_info_t struct, and explain how their values should be determined for a new SoC. Signed-off-by: Andre Przywara <osp@andrep.de>
dlan17
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This doc is really excellent for people to get overview of soc_info structure, so I realize it's not really necessary to get into too many details which takes extra more efforts, or even we can just leave to improve them later.
| - `name`: A string with the short name of the SoC, like `"A133"` or `"T527"`. | ||
| - `spl_addr`: This is the address where the BootROM(BROM) will load an eGON | ||
| wrapped payload to. Often this is the start of the first SRAM block (SRAM A1), | ||
| though newer SoCs tend to deviate here. This must be the same value where the |
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for "must be the same value", it would be great to emphasis this choice is taken by sunxi-tools's policy for easing maintenance, not restricted by lowlevel BROM protocol, which I mean it's totally ok to download code to any valid address and execute..
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It's not OK to load the U-Boot's SPL to a wrong address because it's not position independent.
| SPL binary to work with any load method. | ||
| The SRAM address(es) should be mentioned in the memory map of the manual, but | ||
| it's best to confirm this by loading a small code snippet from SD card and | ||
| printing the load address. |
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is there any public repo available for that small code which able to print the address? or docs recorded for this
(I remember you shared that when I add fel support for A733..)
| out (set to `false`) for every other SoC. | ||
| - `mmu_tt_addr`: Address of some memory area to hold the page tables during | ||
| the FEL operation. Only needed on older SoCs that enable and require the | ||
| MMU during FEL operation. Can be left out (set to 0) for newer SoCs. |
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It's not needed on old SoCs either. But it provided significantly faster data transfer speed. See the detailed explanations in the following commit messages:
e4b3da2, a275b24, c32eeb8. And also the table at https://linux-sunxi.org/FEL/USBBoot#SoC_support_status
The difference between ~180KB/s and ~900KB/s, observed on H3 was gigantic from the practical point of view, considering the typical sizes of the linux kernel images.
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If you have a H3 you should maybe see if DMA works on it. I get nearly a 100x speed increase with that on H616 and ported the optimizations based on BROM dump analysis.
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Add a markdown document describing the basics of the FEL protocol, to give some idea about the expectations and limitations of the protocol.
Also add a description for each member of the soc_info_t struct, and explain how their values should be determined for a new SoC.