[RFC] Layout handling...

[Carl-Daniel Hailfinger]

Hi,

before we change flashrom to work with current layout requirements, we
should summarize the features we need/want, and then decide how to
handle the individual layout regions internally.

Terms:
"write strategy" describes a combination of erase+write commands with a
given block size, touching some blocks.
"read protected" describes a region which can not be read.
"write protected" describes a region which can not be written.
"write once" describes a region which can be written exactly once in the
chip lifetime.

If you add a feature to the list, please give it a nickname so we know
which feature people are referring to. Some of the features below might
not be desirable, but I want to list them anyway so we can explicitly
declare them as unsupported if needed.

fullwrite-unrestricted: Write a chip-sized image, no special read/write
restrictions of the chip, no layout file needs to be specified. Default
write case right now.

fullwrite-noread: Write a chip-sized image, reading anything from the
chip is not possible. Many DVD writers fall in that category. No
verification, violates our reliability guarantees.

fullwrite-postread: Write a chip-sized image, reading anything from the
chip is only possible after write. Chips which are read-locked until a
full erase/write fall in that category. Do those exist as standalone
flash chips or only integrated into processors?

fullwrite-partialread: Write a chip-sized image, reading is only
possible in some chip regions. Only partial verification, violates our
reliability guarantees.

fullwrite-partialwrite: Write a chip-sized image, but writing is only
possible in some regions. This is obviously a conflict unless the image
has the same contents as the chip in the write-protected regions and
there is a possible write strategy for the whole image which does not
touch the write-protected regions. Should flashrom always refuse this
scenario, or only refuse it in case of conflicts?

partialwrite-unrestricted: Write only parts of an image, the rest of the
chip contents is kept, no special read/write restrictions.

partialwrite-partialread: Write only parts of an image, the rest of the
chip contents is kept, reading is only possible in some chip regions. If
no read-protected regions are written and a suitable write strategy
exists, should flashrom warn? If a read-protected region is written,
should flashrom warn/refuse due to reliability requirements?

partialwrite-partialwrite: Write only parts of an image, the rest of the
chip contents is kept, writing is only possible in some chip regions. If
no write-protected regions are written and a suitable write strategy
exists, should flashrom warn? flashrom will refuse to write a
write-protected region.

fullread-unrestricted: Read the full chip, no special read restrictions
of the chip.

partialread-unrestricted: Read only parts of a chip, no special read
restrictions of the chip.

partialread-partialread: Read only parts of a chip, some regions are
read-protected. flashrom should refuse to read any read-protected regions.

partialread-imagefiller: If only parts of a chip are read and the read
image has full chip size, what should be used as filler for unread
regions? 0x00 or 0xff?

partialread-layout-imagesize: If only parts of a chip are read, should
the read image still have full chip size with all read regions filled in
at the respective locations?

partialread-layout-split: If only parts of a chip are read, should it be
possible to write each region (or a combination thereof) to a separate
image file, and would that mapping be specified in the layout file?

partialwrite-layout-split: If only parts of a chip are written, should
it be possible to collect each part of the new image from a separate
image file, and would that mapping be specified in the layout file?

readwrite-protection-time: Which read protection and write protection
times exist? Temporary lock until unlock, temporary lock until chip soft
reset, temporary lock until chip/programmer hard reset (powerdown or
reset line), permanent eternal lock.

readwrite-protection-type: Which read protection and write protection
types exist? Programmer lock (e.g. Intel SPI), hardware chip lock (WP
pin), software chip lock (chip command).

readwrite-protection-interaction: How should we express this situation:
A region is write-locked with a software chip lock, but to remove that
software chip lock, a hardware chip lock has to be disabled first, then
the software chip lock can be disabled.

partialaccess-crash: Some regions in the chip are really off-limits and
will cause an unrecoverable error (system crash) when accessed (read or
write). That seems to be the case for some EC/flash interactions.

Comments? Any forks of flashrom (e.g. chromium) which need
infrastructure features not mentioned above?

Regards,
Carl-Daniel