Enumeration & Link Training: Interview · protocols

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Should a driver put a CPU virtual pointer directly into a DMA descriptor because its BAR registers are accessible?

Check yourself Should a driver put a CPU virtual pointer directly into a DMA descriptor because its BAR registers are accessible?

No. Use the platform DMA mapping API and the resulting device address; BAR accessibility does not establish DMA address translation or permissions.

Common trap: Giving a generic fix without identifying the boundary and unmet obligation in this example.

LTSSM reached L0 but width is wrong — what next?

Check yourself LTSSM reached L0 but width is wrong — what next?

Read LTSSM history and negotiated capabilities, compare configured limits, then inspect lane training and physical margins. Compare reset, clocks, firmware settings and channel conditions between boards. A lane fault is one possible cause, but reduced width alone does not prove it.

Common trap: Blaming enumeration software first.

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