On Wed, 10 Jul 2013, Geert Uytterhoeven wrote:
> If NO_DMA=y:
>
> drivers/built-in.o: In function `usb_hcd_unmap_urb_setup_for_dma':
> drivers/usb/core/hcd.c:1361: undefined reference to `dma_unmap_single'
> ,,,
>
> Commit d9ea21a779278da06d0cbe989594bf542ed213d7 ("usb: host: make
> USB_ARCH_HAS_?HCI obsolete") allowed to enable USB on platforms with
> NO_DMA=y, and exposed several input and media USB drivers that just select
> USB if USB_ARCH_HAS_HCD, without checking HAS_DMA.
>
> Fix the former by making USB depend on HAS_DMA.
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.
> To fix the latter, instead of adding lots of "depends on HAS_DMA", make
> those drivers depend on USB, instead of depending on USB_ARCH_HAS_HCD and
> selecting USB. Drivers for other busses (e.g. MOUSE_SYNAPTICS_I2C) already
> handle this in a similar way.
That seems reasonable.
Alan Stern
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