> + Compatible strings can be either explicit vendor names and part numbers > + (e.g. elpida,ECB240ABACN), or generated strings of the form > + (lp)?ddrX-Y,Z where X, Y and Z are in lower case hexadecimal with leading > + zeroes and : > + - X is the SDRAM version (2, 3, 4, etc.) > + - for LPDDR : > + - Y is the manufacturer ID (from MR5), 2 bytes > + - Z is the revision ID (from MR6 and MR7), 4 bytes It's actually one byte manufacturer, two bytes revision. The YY,ZZZZ is supposed to represent the amount of hex digits needed. > + - for DDR4 with SPD, according to JEDEC SPD4.1.2.L-6 : > + - Y is the manufacturer ID, 2 bytes, from bytes 320 and 321 > + - Z is the revision ID, 1 byte, from byte 349 I don't think this will identify a part unambiguously, I would expect the DDR revision ID to be specific to the part number. (In fact, we're also not sure whether manufacturer+revision identifies LPDDR parts unambiguously for every vendor, we just didn't have anything more to work with there.) I would suggest to use either `ddrX-YYYY,AAA...,ZZ` or `ddrX-YYYY,ZZ,AAA...` (where AAA... is the part number string from SPD 329-348 without the trailing spaces). The first version looks a bit more natural but it might get confusing on the off chance that someone uses a comma in a part number string. > + The latter form can be useful when SDRAM nodes are created at runtime by > + boot firmware that doesn't have access to static part number information. nit: This text slightly doesn't make sense anymore when in the DDR case we do actually have the part number. I guess the real thing the bootloader wouldn't have access to is the JEDEC manufacturer ID to name mapping. > + SDRAM revision ID: > + - LPDDR SDRAM, decoded from Mode Register 6 and 7. > + - DDR4 SDRAM, decoded from the SPD from bytes 349 according to > + JEDEC SPD4.1.2.L-6. nit: Clarify that this is always two bytes for LPDDR and always one byte for DDR. > + Density of SDRAM chip in megabits: > + - LPDDR SDRAM, decoded from Mode Register 8. > + - DDR4 SDRAM, decoded from the SPD from bytes 322 to 325 according to > + JEDEC SPD4.1.2.L-6. Are these numbers correct? I downloaded SPD4.1.2.L-6 now and it looks like 322 is manufacturing location and 323-324 are manufacturing date. (Also, I think all of these are specific to DDR4 (and possibly 5?), but not to earlier versions. I don't think we need to list it for every version, but we should at least be specific what it applies to.)
