Claude review: drm/imagination: Fix deadlock in soft reset sequence

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Correctness: Good.**

The call chain is confirmed:
1. `pvr_device_irq_thread_handler()` (`pvr_device.c:203`) — threaded IRQ handler
2. → `pvr_fwccb_process()` (`pvr_device.c:217`)
3. → `process_fwccb_command()` (`pvr_ccb.c:196`)
4. → `pvr_power_reset(pvr_dev, false)` (`pvr_ccb.c:149`)

Inside `pvr_power_reset`, the original code unconditionally called `disable_irq()`, which invokes `synchronize_irq()` internally, deadlocking because the threaded handler is waiting for itself to complete.

The fix:
```c
if (hard_reset) {
    disable_irq(pvr_dev->irq);
} else {
    /*
     * Soft reset is triggered as a response to a FW command to the Host and is
     * processed from the threaded IRQ handler. This code cannot (nor needs to)
     * wait for any IRQ processing to complete.
     */
    disable_irq_nosync(pvr_dev->irq);
}
```

This is correct. `disable_irq_nosync()` still increments the IRQ disable depth counter, preventing new IRQs from being delivered, but doesn't call `synchronize_irq()`. Since we're already running *as* the threaded handler, there's no concurrent IRQ processing to wait for.

**Soft-to-hard escalation path: Correct.** When a soft reset fails (`pvr_power.c:559-562`), the code sets `hard_reset = true` and loops. The IRQ is already disabled (via `_nosync`), and the loop proceeds to do the hard reset with IRQs still disabled. At completion, `enable_irq()` at line 568 re-enables correctly regardless of which `disable_irq` variant was used, since both increment the same disable depth counter.

**Comment quality: Good.** The comment clearly explains why `disable_irq_nosync()` is used and why it's safe.

**Minor observation (non-blocking):** The hard reset callers (`pvr_power.c:209` in the watchdog, `pvr_mmu.c:169`) appear to run from non-IRQ context, so `disable_irq()` remains correct for that path.

No issues found. The patch is clean, minimal, and correct.

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