GEN8_CTX_ID_WIDTH
(1U << (GEN8_CTX_ID_WIDTH - 1)) - 1;
(1U << GEN8_CTX_ID_WIDTH) - 1;
BUILD_BUG_ON(MAX_CONTEXT_HW_ID > (BIT(GEN8_CTX_ID_WIDTH)));
GEM_BUG_ON(ctx->hw_id >= BIT(GEN8_CTX_ID_WIDTH));