From: Arnd Bergmann <arnd@arndb.de>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
linux-input@vger.kernel.org, linux-media@vger.kernel.org,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] usb: USB host support should depend on HAS_DMA
Date: Thu, 11 Jul 2013 01:12:56 +0200 [thread overview]
Message-ID: <201307110112.57398.arnd@arndb.de> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1307101724430.1215-100000@iolanthe.rowland.org>
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
next prev parent reply other threads:[~2013-07-10 23:13 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-10 21:18 [PATCH] usb: USB host support should depend on HAS_DMA Geert Uytterhoeven
2013-07-10 21:31 ` Alan Stern
2013-07-10 23:12 ` Arnd Bergmann [this message]
2013-07-11 1:01 ` Alan Stern
2013-07-11 7:49 ` Geert Uytterhoeven
2013-07-11 15:03 ` Alan Stern
2013-08-18 21:12 ` Geert Uytterhoeven
2013-08-19 15:09 ` Alan Stern
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