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

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Message-ID: <47811770.4040706@s5r6.in-berlin.de>
Date:	Sun, 06 Jan 2008 19:01:20 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Al Boldi <a1426z@...ab.com>
CC:	Sam Ravnborg <sam@...nborg.org>, Adrian Bunk <bunk@...nel.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Brownell <david-b@...bell.net>, Greg KH <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/5] USB Kconfig: Select SCSI for USB Mass Storage support

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
-=====-==--- ---= --==-
http://arcgraph.de/sr/
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