Re: [PATCH 2/5] USB Kconfig: Select SCSI for USB Mass Storage support

Stefan Richter
2008-01-06T18:02:16Z

Stefan Richter wrote:
> Al Boldi wrote:
>> Stefan Richter wrote:
>>> Still wrong. SCSI also needs HAS_DMA and SCSI_DMA.
>> I don't think so. SCSI selects SCSI_DMA, it doesn't depend on it.
>
> "A selects B" == "A depends on B, but please don't hide A when B is off
> and silently switch B on when A is switched on".
>
> config SCSI
> tristate "SCSI device support"
> depends on BLOCK
> select SCSI_DMA if HAS_DMA
>
> So, SCSI doesn't actually need SCSI_DMA per se, but it apparently needs
> it whenever HAS_DMA != n.

In fact, only a number of SCSI low-level drivers need SCSI_DMA. But
libata and usb-storage are currently not among those drivers. For them
it's currently harmless if SCSI_DMA is off.

SCSI_DMA only includes the symbols scsi_dma_map() and scsi_dma_unmap()
into the scsi core. libata and usb-storage don't call these.
--
Stefan Richter
-=====-==--- ---= --==-