# DF-3976 — Inverted error check in btc_dpm_init: computed PLL reference divider used only when radeon_atom_get_clock_dividers FAILS

- File: `sys/dev/drm/radeon/btc_dpm.c:2602-2607`
- Class: CWE-670 wrong logic (Info) — family: DF-3652 (ci inverted return). Functional/hardening,
  no memory-safety impact.

## Code

```c
ret = radeon_atom_get_clock_dividers(rdev, COMPUTE_ENGINE_PLL_PARAM,
				     0, false, &dividers);
if (ret)
	pi->ref_div = dividers.ref_div + 1;   /* used on FAILURE */
else
	pi->ref_div = R600_REFERENCEDIVIDER_DFLT;  /* default on SUCCESS */
```

`radeon_atom_get_clock_dividers()` returns 0 on success; on failure it has already memset dividers
to zero (radeon_atombios.c:2838), so the failure arm programs `pi->ref_div = 1`, and the success arm
discards the computed `dividers.ref_div`. Compare the correct pattern in the same tree
(ni_dpm.c:2015-2020: `if (ret) return ret;` then use dividers).

## Impact

`pi->ref_div` feeds MPLL lock-time programming (`rv770_dpm.c:815`,
`MPLL_LOCK_TIME(R600_MPLLLOCKTIME_DFLT * pi->ref_div)`): on an ATOM command failure the lock time is
programmed 12x too short (ref_div=1 vs default 12) — marginal memory-clock PLL locking / display
instability. No memory-safety impact (dividers is stack memory but pre-zeroed by the callee, so no
uninitialized read reaches it). Info severity, matching DF-3652's treatment of the analogous
inverted return.