Re: [PATCH/RFC 0/6] Allow compile-testing NO_DMA

Robin Murphy <robin.murphy@xxxxxxx> · Tue, 6 Feb 2018 13:05:44 +0000

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@xxxxxxx>

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(-)