On Wednesday 10 July 2013, Alan Stern wrote:
> This isn't right. There are USB host controllers that use PIO, not
> DMA. The HAS_DMA dependency should go with the controller driver, not
> the USB core.
>
> On the other hand, the USB core does call various routines like
> dma_unmap_single. It ought to be possible to compile these calls even
> when DMA isn't enabled. That is, they should be defined as do-nothing
> stubs.
The asm-generic/dma-mapping-broken.h file intentionally causes link
errors, but that could be changed.
The better approach in my mind would be to replace code like
if (hcd->self.uses_dma)
with
if (IS_ENABLED(CONFIG_HAS_DMA) && hcd->self.uses_dma) {
which will reliably cause that reference to be omitted from object code,
but not stop giving link errors for drivers that actually require
DMA.
Arnd
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