The GSoC coding period has started and I have been working on my first sub-project, adding support for 2nd status register. Most supported chips that have multiple registers (around 80%) have opcode 0x35 for reading SR2 and, opcode 0x01 for writing SR2. I have developed 3 models and would like to have some feedback on them.
1. Integrate read/write SR2 with existing functions PROPOSAL - - Define a feature bit FEATURE_SR2 - spi_read_status_register(), defined in spi25_statusreg.c, additionally reads second status register depending on FEATURE_SR2 bit for that flash - Change return to uint16_t for spi_read_status_register() - spi_write_status_register_flag(), defined in spi25_statusreg.c, considers higher byte of status to write to SR2, depending on FEATURE_SR2 bit for that flash. MERITS - - Fits in elegantly with existing implementation (IMO). Most code in flashrom stores status reads/writes in int, which can easily accommodate the 16 bits - Very little hassle when editing struct flashchip in flashchips.c
DEMERITS - - RDSR will take more time - will read SR2 even if not needed
2. Define separate functions to read/write SR2 PROPOSAL - - Define spi_read_status_register2() to read only SR2 - Define spi_write_status_register2_flag() and spi_write_status_register2() to write to SR2. This will read SR1 first, then (SR2 << 8 | SR1) will be written using WRSR
MERITS - - Flexibility (as compared to 1.)
DEMERITS - - Need to write more lines (compared to 1.) when dealing with struct flashchip
3. struct status_register_layout The ChromiumOS fork defines a struct status_register_layout in writeprotect.c, which contains only BP and SRP bits' information. PROPOSAL - Do a similar flashrom-wide definition, which contains all status register bits' information.
MERITS - - Very detailed representation of information
DEMERITS - - Too much work when adding support for new chips - Overhaul of existing infrastructure
IMHO, the first model is the best among these 3. I would like to know what you guys think about these, whether you have some new idea. Looking forward to your feedback. Thanks for your time.