Albert Lee wrote:
> Some devices raise irq early before clearing the BSY.
> This patch waits up to 10 microseconds to workaround the early irq problem.
>
BTW, the patch is on the hot path. The following is a quick analysis of
the performance penalty introduced by the patch:
1. DMA mode:
The dma_status is checked before reading the alt_status, so we are pretty
sure that it is our interrupt. It's worthwhile to poll alt_status and wait
for BSY to clear in this case.
2. PIO mode with non-shared irq:
It is our interrupt. It's worthwhile to wait a moment for BSY to clear.
3. PIO mode with shared-irq:
If PIO + shared-irq + qc active + other people's irq
=> We waste 10 micro seconds to figure out that it is not our interrupt.
In exchange for the wasted time, we get better tolerance for the
early irq situations.
--
albert
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