[flashrom] Giving to -i option some real use

[David Hendricks]

On Thu, Apr 21, 2016 at 1:41 PM, Salvador Eduardo Tropea <
salvador at inti.gob.ar> wrote:

> Hi David:
>
> Thanks for your comments.
>
>
> El 20/04/16 a las 20:42, David Hendricks escribió:
>
>> Hello Salvador,
>> Yes, this is a very useful feature - we've had it in the chromiumos
>> branch for a while now :-)
>>
>> I need to read your implementation. Ours is called "fast-verify" which
>> will read and only verify portions of the flash specified with -i arguments.
>>
>
> What about writes? My problem is that I have a 4 MiB flash and that
> usually need to use 32kB from it.


Yes, it works for writes as well. Using your layout file as an example:
00000000:00007e2b fpga
00007e2c:003fffff free

If the eraseblock size is 4KB and you run *"*flashrom -p <programmer> -l
layout -i fpga -w foo.bin --fast-verify*"*, chromium's flashrom will:
1. Detect the flash chip.
2. Parse the -i argument
3. Do a partial read. This is broken into a multiple steps.
3a. Determine the "required_erase_size", for example, 4KB. Right now the
mechanism is crude and chooses the smallest block size that is eraseable.
3b. Align regions that are read based on required_erase_size. 0000 is
already aligned, but 7e2b will be aligned up to 7fff.
3c. Read the aligned region content, which is 0000:7fff instead of
0000:7e2b, into the new content buffer.
4. Copy the new content from the "fpga" region into the new content buffer.
5. Erase and write 0000:7fff
6. Verify from 0000:7fff

Overall it looks pretty similar to what you posted. Here's the original
implementation: https://chromium-review.googlesource.com/#/c/240176/
<https://chromium-review.googlesource.com/#/c/240176/4>. There are a couple
of follow-up patches as well, in case you're interested.

One more thing to note - Be careful about interactions with the proposed
patch to read the current contents of flash from a file:
https://www.flashrom.org/pipermail/flashrom/2015-December/014034.html.
Specifically, make sure that the aligned offsets are used for reading old
content no matter if the old content is in a flash chip or a file.

-- 
David Hendricks (dhendrix)
Systems Software Engineer, Google Inc.
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