char: xillybus: Harden driver and improve code quality

This patch set consists of several boundary and sanity checks, gaining
better control of execution flow and fixing minor coding issues. No
difference is expected in the driver's behavior under normal conditions,
except for one change that might improve bandwidth performance
marginally.

Why all of the sudden? These patches are the result of a comprehensive
AI-assisted code review, using Deepseek, Kimi Thinking K2.6, ChatGPT,
and Claude Sonnet 4.6 as plain prompt tools.

I've spent three weeks in what I call a "reverse rubber duck" session,
asking these LLMs to find bugs in the code and following up on different
leads, the vast majority of which turned out to be no more than quack.
Occasionally the points made by AI were valid, and in others, the mere
effort to explain why the remark is wrong to the rubber duck led to
finding real issues.

Almost none of the fixes suggested by AI were even near the actual
corrections in this patch set.

Thanks & regards,
   Eli

Eli Billauer (7):
  char: xillybus: Improve control of execution flow with mutexes
  char: xillybus: Remove duplicate error path code
  char: xillybus: Avoid possible bandwidth inefficiency
  char: xillybus: Use unsigned arithmetic for jiffies differences
  char: xillybus: Integer arithmetic improvements
  char: xillybus: Add defensive sanity checks
  char: xillybus: Ignore and report unsolicited interrupts

 drivers/char/xillybus/xillybus.h       |   3 +
 drivers/char/xillybus/xillybus_class.c |  11 +++
 drivers/char/xillybus/xillybus_class.h |   4 +
 drivers/char/xillybus/xillybus_core.c  | 100 ++++++++++++++++++++++---
 drivers/char/xillybus/xillybus_of.c    |   6 ++
 drivers/char/xillybus/xillyusb.c       |  62 +++++++++++----
 6 files changed, 160 insertions(+), 26 deletions(-)

-- 
2.34.1