Claude review: dma-buf: Add the SGT DMA mapping type

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

Patch Review

> +enum dma_sgt_requires_p2p {
> +	DMA_SGT_NO_P2P = 0,
> +	DMA_SGT_EXPORTER_REQUIRES_P2P_DISTANCE,
> +	DMA_SGT_IMPORTER_ACCEPTS_P2P,
> +};

A single enum serves double duty for `exporter_requires_p2p` and `importer_accepts_p2p`. The naming of the enum values tries to prevent misuse, but the type system doesn't enforce it. Nothing stops setting `exporter_requires_p2p = DMA_SGT_IMPORTER_ACCEPTS_P2P`, which would silently fall through the switch to return 0 (match succeeds). Would separate enums or booleans be clearer?

> +	switch (exp->sgt_data.exporter_requires_p2p) {
> +	case DMA_SGT_NO_P2P:
> +		return 0;
> +	case DMA_SGT_EXPORTER_REQUIRES_P2P_DISTANCE:
> +		...
> +	}
> +	return 0;

The default fall-through silently accepts any value. A `WARN_ON_ONCE` or explicit default handling would catch programming errors.

> +		u8 importer_accepts_p2p;
> +		u8 exporter_requires_p2p;

These are `u8` rather than `enum dma_sgt_requires_p2p`. Intentional for size, or an oversight?

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