My scanner is an all in one HP photosmart C6380 (driver photosmart C6300).
With hplip version 3.12.6, no resolution is available for scanning.
I just tested every version since mga1 and the bug appeared with version 3.12.4 ; 3.12.2 is OK.
It's still present with 3.12.9.
Here is interesting part of trace with hp-scan (complete trace as attachment) :
hp-scan: debug: Device supported resolutions [75, 100, 150, 200, 300, 600, 1200, 2400, 4800]
Scan area (mm):
Top left (x,y): (0.000000mm, 0.000000mm)
Bottom right (x,y): (215.899994mm, 296.925995mm)
error: Unable to set option resolution to value 300
hp-scan: debug: Supported source Options:  size=0
error: Unable to set option source to value Flatbed
warning: File destination enabled with no output file specified.
Setting output format to PNG for greyscale mode.
warning: Defaulting to '/home/jules/rpm/cauldron/hplip/RPMS/x86_64/hpscan001.png'.
Debian bug reports for the same problem :
Created attachment 2877 [details]
Complete trace of hp-scan
It seems it's a bogus value in file /usr/share/hplip/data/models/models.dat
in section photosmart_c6300_series, replace scan-src=2 by scan-src=1 and, at least for me, it solves the problem.
Created attachment 2908 [details]
Proposed patch against hplip 3.12.9 to fix this bug
Forget to say the answer come from a dev on launchpad :
This bug is fixed in just released hplip-3.12.10 :
so cauldron should be fine as soon as this version is pushed.
Can we get an update for mga2 ?
Outstanding hplip update cannot be pushed: https://bugs.mageia.org/show_bug.cgi?id=5395
So if you help in validating that one, i can add this patch to it, so we fix two bugs with one update.
Could you please check hplip-3.12.10-1.mga4 which was pushed to cauldron? Should hit mirrors soon, if it fixes the issue this could be pushed to Mageia 3, not sure about Mageia 2.
Sorry I couldn't test sooner.
The latest package in cauldron (3.12.11-1) fix the bug and does seems to work in mga3.
This message is a reminder that Mageia 2 is nearing its end of life.
Approximately one month from now Mageia will stop maintaining and issuing updates for Mageia 2. At that time this bug will be closed as WONTFIX (EOL) if it remains open with a Mageia 'version' of '2'.
Package Maintainer: If you wish for this bug to remain open because you plan to fix it in a currently maintained version, simply change the 'version' to a later Mageia version prior to Mageia 2's end of life.
Bug Reporter: Thank you for reporting this issue and we are sorry that we may not be able to fix it before Mageia 2 is end of life. If you would still like to see this bug fixed and are able to reproduce it against a later version of Mageia, you are encouraged to click on "Version" and change it against that version of Mageia.
Although we aim to fix as many bugs as possible during every release's lifetime, sometimes those efforts are overtaken by events. Often a more recent Mageia release includes newer upstream software that fixes bugs or makes them obsolete.
The Mageia Bugsquad
Mageia 2 changed to end-of-life (EOL) status on ''22 November''. Mageia 2 is no
longer maintained, which means that it will not receive any further security or
bug fix updates. As a result we are closing this bug.
If you can reproduce this bug against a currently maintained version of Mageia
please feel free to click on "Version" change it against that version of Mageia
and reopen this bug.
Thank you for reporting this bug and we are sorry it could not be fixed.
The Mageia Bugsquad