DF-3870 — bw_calcs_init: number_of_dram_channels = vram_width / dram_channel_width can be 0

dce_calcs.c:2041/2157/2270/2386/2502/2615 (every asic table):

vbios.number_of_dram_channels = asic_id.vram_width / vbios.dram_channel_width_in_bits;

asic_id.vram_width comes from amdgpu gmc_v7/v8 (atombios or MC-register fallback). If a part reports a vram_width smaller than the per-table channel width (64 for CZ/Stoney, 32 for Polaris, 128 for Vega10 HBM) — e.g. 32 on a Carrizon-class part — the division truncates to 0 channels.

data->number_of_dram_channels (dce_calcs.c:591) is then used as a multiplier-turned-divisor at dce_calcs.c:1185/1187 (dmif/mcifwr burst time), 1526/1532/1540/1546/1552/1557 (dram_bandwidth), i.e. bw_div(..., bw_int_to_fixed(0)) -> bw_frc_to_fixed(n, 0) -> div64_u64_rem(n, 0) -> kernel #DE panic at the first mode validation after boot.

Also inefficient_linear_pitch_in_bytes = 256*banks*channels (1050) becomes 0 -> bw_mod(pitch, 0) (1098) is a second zero-divisor on the same value.

Hardware/VBIOS-gated (needs a misdetecting board); reported as Low.

DF-3870 VERDICT — inconclusive (hardware/VBIOS-gated), speculative

• Source chain verified: dce_calcs.c:2041 (etc.) integer division truncation; gmc_v8_0.c:525-568 (atombios value, MC-register fallback) — a zero or sub-channel-width detection survives into bw_calcs_init; no clamp exists anywhere between amdgpu_device and the bw tables.
• Divisor sites confirmed by reading calculate_bandwidth: 1185, 1187, 1526, 1532, 1540, 1546, 1552, 1557 (bw_int_to_fixed(data->number_of_dram_channels)) and bw_mod at 1098.
• Cannot be exercised on the guest (no AMD HW); real boards normally report a sane width, hence speculative/Low. Defensive clamp is one line (fix.diff).

Fix status (batch validation)

Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest make -j6 nativekernel KERNCONF=X86_64_GENERIC completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.