Wolfgang Denk wrote:
In message 46500875.6060706@grandegger.com you wrote:
CFG_FDT_ADDR_FLASH: If defined, "fdt" is set to that address at compile time. The FDT can be used from the early beginning of the boot.
Just nitpicking: maybe we should call this CFG_FDT_ADDR_STATIC or CFG_FDT_ADDR_DEFAULT or CFG_FDT_ADDR_INIT or something like that. Rationale: flash is just one of the possible storage devies - it could be ROM instead, or even RAM in certain configurations.
Also, while we are defining this, please keep in mind that sooner or later someone will come up with the idea of storing the FDT in EEPROM, so we might want to reserve such identifiers.
Good points, I agree with them. One possibility would be to name it CFG_FDT_ADDR_INIT (my 2c for name choice) and #define it to a static address for the typical flash storage case and #define it to be a function that returns an address for the read-from-EEPROM case.
CFG_FDT_ADDR_BY_ENV: If defined, the env variable "fdtaddr" is looked up early in the boot and "fdt" is set accordingly. This allows to hold more than one blob in FLASH and select one via env setting. This would allow for _one_ combination of images of U-Boot + Linux + Blobs for a _set_ of boards.
Traditionally, that should be named CFG_FDT_ADDR_IN_ENV
Ditto.
CFG_FDT_ADDR_RAM: If defined, the blob is moved to RAM after relocation for further preparation or for performance reasons. "fdt" is re-set accordingly. The blob is then ready and in place for booting Linux. If CFG_FDT_ADDR_RAM is set to 0, the blob will be copied to a default location, e.g. before the initrd location.
I'm not sure I understand this - will CFG_FDT_ADDR_RAM hold the *address* in RAM where the FDT gets copied to? That sounds pretty static to me.
This would be used if the blob has to be copied out of flash into RAM (or could be part of the read-from-EEPROM usage).
I'm not sure this is necessary (echoing wd's "pretty static" reaction). The board-specific code in the start up should know where a good place to place the RAM copy of the blob is, for instance, right after the RAM copy of u-boot. Is there a case where it _must_ be a fixed address? I cannot think of any.
If there is a case where it _must_ be fixed, it seems to me it would be so unusual a case that I would leave it up to the board supporter to hardcode it in the board-specific start up.
My gut feel is to not document/define a CFG_FDT_ADDR_RAM until we get use cases that show that it is a Good Thing[tm].
A board-specific checkboad function is called as early as possible to verify the FDT.
"checkboard()" is a name that can mean anything. If the function is to check or to verify the FDT, the function name should represent this, i. e. please callit checkfdt() or verifyfdt() of probably fdtcheck() / fdtverify() or fdt_check() / fdt_verify().
I'm somewhat skeptical about the fdt_checkboard() concept, how well it would work in practice. If the blob is for the wrong board, will the serial work? Sometimes yes, sometimes no. For the times the answer is "yes", the ability is probably worth considering, at least.
I would like to see the verification/validation that we currently do on the env data to be done on the blob as well. This is heading towards my assertion that the blob can take over most, perhaps all, of the duties of the current "env" storage. Not all of the thoughts below are directly on topic since I'm expanding beyond just u-boot config. * A CRC * Backup copy (if selected in the board config) * Default compiled in copy (?) * Likely not useful since, by definition, some parts of the fdt would be board specific and not detectable by the board start up code. * Hmm, if we had a minimal default compiled in copy, we could compare its values to a user-loadable version as (part of) a fdt_checkboard() function.
Best regards, Wolfgang Denk
Ditto, gvb