Claude review: drm/gem-dma: Add flag for bidirectional mapping of non-coherent GEM DMA buffers

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

Patch Review

The approach works but adding a second boolean for what is essentially a direction parameter is inelegant. Consider replacing the pair (`map_noncoherent` + `map_bidirectional`) with a single `enum dma_data_direction` field, or at minimum a `dma_data_direction map_dir` that drivers set directly. This would be cleaner and more extensible.

That said, the current code is functionally correct. The `drm_gem_dma_mmap()` path for noncoherent uses `dma_mmap_pages()` which doesn't take a direction, so no changes needed there.

One concern: `map_bidirectional` is only meaningful when `map_noncoherent` is true, but nothing enforces this. If a driver sets `map_bidirectional = true` without `map_noncoherent = true`, the flag is silently ignored. The doc comment says "valid only if map_noncoherent flag is set" but there's no runtime check. A `WARN_ON` or at least asserting the invariant would be safer.

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Generated by Claude Code Patch Reviewer