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Date: Tue, 6 Feb 2018 13:05:44 +0000
From: Robin Murphy <robin.murphy@....com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>,
Christoph Hellwig <hch@....de>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Arnd Bergmann <arnd@...db.de>, Mark Brown <broonie@...nel.org>,
Richard Weinberger <richard@....at>
Cc: Felipe Balbi <balbi@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
"Martin K . Petersen" <martin.petersen@...cle.com>,
iommu@...ts.linux-foundation.org, linux-usb@...r.kernel.org,
linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org
Subject: Re: [PATCH/RFC 0/6] Allow compile-testing NO_DMA
On 06/02/18 10:14, Geert Uytterhoeven wrote:
> Hi all,
>
> If NO_DMA=y, get_dma_ops() returns a reference to the non-existing
> symbol bad_dma_ops, thus causing a link failure if it is ever used.
>
> The intention of this is twofold:
> 1. To catch users of the DMA API on systems that do no support the DMA
> mapping API,
> 2. To avoid building drivers that cannot work on such systems anyway.
>
> However, the disadvantage is that we have to keep on adding dependencies
> on HAS_DMA all over the place.
>
> Thanks to the COMPILE_TEST symbol, lots of drivers now depend on one or
> more platform dependencies (that imply HAS_DMA) || COMPILE_TEST, thus
> already covering intention #2. Having to add an explicit dependency on
> HAS_DMA here is cumbersome, and hinders compile-testing.
>
> Hence I think the time is ripe to reconsider the link failure.
> This patch series:
> - Changes get_dma_ops() to return NULL instead,
> - Adds a few more dummies to enable compile-testing,
> - Removes dependencies on HAS_DMA for symbols that already have
> platform dependencies implying HAS_DMA.
>
> Note that adding more platform dependencies and/or dependencies on
> COMPILE_TEST is encouraged!
>
> This may make life harder for UML, though, as UML usually satisfies all
> other platform dependencies for HAS_DMA. Similarly, HAS_IOMEM is even
> more complicated. Can/do we want to do something similar for
> HAS_IOMEM?
It looks like we have only one real arch (score) without IOMEM, and two
(s390 and tile) where it is possible to configure out, so it does seem
like a reasonable feature to assume. Maybe we could have something like
asm-generic/no-io.h to provide an "unimplemented" version of those
interfaces.
Anyway, for this series:
Acked-by: Robin Murphy <robin.murphy@....com>
Thanks,
Robin.
> This series is against my current local tree, which has a few more
> "depends on HAS_DMA" than upstream. Of course I will rebase, and split
> the last patch per subsystem, if this RFC is welcomed positively.
>
> Compile-tested with allmodconfig and allyesconfig for m68k/sun3.
>
> Thanks for your comments!
>
> Geert Uytterhoeven (6):
> [RFC] dma-mapping: Convert NO_DMA get_dma_ops() into a real dummy
> [RFC] dma-coherent: Add NO_DMA dummies for managed DMA API
> [RFC] usb: gadget: Add NO_DMA dummies for DMA mapping API
> [RFC] mm: Add NO_DMA dummies for DMA pool API
> [RFC] scsi: Add NO_DMA dummies for SCSI DMA mapping API
> [RFC] Treewide: Remove depends on HAS_DMA in case of platform
> dependency
>
> drivers/ata/Kconfig | 2 --
> drivers/crypto/Kconfig | 14 +++------
> drivers/firewire/Kconfig | 1 -
> drivers/fpga/Kconfig | 1 -
> drivers/gpu/ipu-v3/Kconfig | 1 -
> drivers/i2c/busses/Kconfig | 3 --
> drivers/iio/adc/Kconfig | 3 --
> drivers/iommu/Kconfig | 5 ++--
> drivers/lightnvm/Kconfig | 2 +-
> drivers/mailbox/Kconfig | 2 --
> drivers/media/pci/dt3155/Kconfig | 1 -
> drivers/media/pci/solo6x10/Kconfig | 1 -
> drivers/media/pci/sta2x11/Kconfig | 1 -
> drivers/media/pci/tw5864/Kconfig | 1 -
> drivers/media/pci/tw686x/Kconfig | 1 -
> drivers/media/platform/Kconfig | 40 ++++++++-----------------
> drivers/media/platform/am437x/Kconfig | 2 +-
> drivers/media/platform/atmel/Kconfig | 4 +--
> drivers/media/platform/blackfin/Kconfig | 1 -
> drivers/media/platform/davinci/Kconfig | 6 ----
> drivers/media/platform/marvell-ccic/Kconfig | 3 +-
> drivers/media/platform/rcar-vin/Kconfig | 2 +-
> drivers/media/platform/soc_camera/Kconfig | 3 +-
> drivers/media/platform/sti/c8sectpfe/Kconfig | 2 +-
> drivers/mmc/host/Kconfig | 10 ++-----
> drivers/mtd/nand/Kconfig | 8 ++---
> drivers/mtd/spi-nor/Kconfig | 2 +-
> drivers/net/ethernet/amd/Kconfig | 2 +-
> drivers/net/ethernet/apm/xgene-v2/Kconfig | 1 -
> drivers/net/ethernet/apm/xgene/Kconfig | 1 -
> drivers/net/ethernet/arc/Kconfig | 6 ++--
> drivers/net/ethernet/broadcom/Kconfig | 2 --
> drivers/net/ethernet/calxeda/Kconfig | 2 +-
> drivers/net/ethernet/hisilicon/Kconfig | 2 +-
> drivers/net/ethernet/marvell/Kconfig | 8 ++---
> drivers/net/ethernet/mellanox/mlxsw/Kconfig | 2 +-
> drivers/net/ethernet/renesas/Kconfig | 2 --
> drivers/net/ethernet/socionext/Kconfig | 4 +--
> drivers/net/wireless/broadcom/brcm80211/Kconfig | 1 -
> drivers/net/wireless/quantenna/qtnfmac/Kconfig | 2 +-
> drivers/remoteproc/Kconfig | 1 -
> drivers/scsi/hisi_sas/Kconfig | 2 +-
> drivers/spi/Kconfig | 12 ++------
> drivers/staging/media/davinci_vpfe/Kconfig | 1 -
> drivers/staging/media/omap4iss/Kconfig | 1 -
> drivers/staging/vc04_services/Kconfig | 1 -
> drivers/tty/serial/Kconfig | 4 ---
> drivers/usb/gadget/udc/Kconfig | 4 +--
> drivers/usb/mtu3/Kconfig | 2 +-
> drivers/video/fbdev/Kconfig | 3 +-
> include/linux/dma-mapping.h | 19 ++++++++----
> include/linux/dmapool.h | 21 +++++++++++--
> include/linux/usb/gadget.h | 12 ++++++++
> include/scsi/scsi_cmnd.h | 5 ++++
> sound/soc/bcm/Kconfig | 3 +-
> sound/soc/kirkwood/Kconfig | 1 -
> sound/soc/pxa/Kconfig | 1 -
> sound/soc/qcom/Kconfig | 6 ++--
> 58 files changed, 108 insertions(+), 148 deletions(-)
>
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