[PATCH v3] drivers: introduce and use WANT_DMA_CMA for soft dependencies on DMA_CMA

Fri Apr 9 22:30:34 AEST 2021

Am Freitag, dem 09.04.2021 um 13:20 +0200 schrieb David Hildenbrand:
> Random drivers should not override a user configuration of core knobs
> (e.g., CONFIG_DMA_CMA=n). Applicable drivers would like to use DMA_CMA,
> which depends on CMA, if possible; however, these drivers also have to
> tolerate if DMA_CMA is not available/functioning, for example, if no CMA
> area for DMA_CMA use has been setup via "cma=X". In the worst case, the
> driver cannot do it's job properly in some configurations.
> 
> For example, commit 63f5677544b3 ("drm/etnaviv: select CMA and DMA_CMA if
> available") documents
> 	While this is no build dependency, etnaviv will only work correctly
> 	on most systems if CMA and DMA_CMA are enabled. Select both options
> 	if available to avoid users ending up with a non-working GPU due to
> 	a lacking kernel config.
> So etnaviv really wants to have DMA_CMA, however, can deal with some cases
> where it is not available.
> 
> Let's introduce WANT_DMA_CMA and use it in most cases where drivers
> select CMA/DMA_CMA, or depend on DMA_CMA (in a wrong way via CMA because
> of recursive dependency issues).
> 
> We'll assume that any driver that selects DRM_GEM_CMA_HELPER or
> DRM_KMS_CMA_HELPER would like to use DMA_CMA if possible.
> 
> With this change, distributions can disable CONFIG_CMA or
> CONFIG_DMA_CMA, without it silently getting enabled again by random
> drivers. Also, we'll now automatically try to enabled both, CONFIG_CMA
> and CONFIG_DMA_CMA if they are unspecified and any driver is around that
> selects WANT_DMA_CMA -- also implicitly via DRM_GEM_CMA_HELPER or
> DRM_KMS_CMA_HELPER.
> 
> For example, if any driver selects WANT_DMA_CMA and we do a
> "make olddefconfig":
> 
> 1. With "# CONFIG_CMA is not set" and no specification of
>    "CONFIG_DMA_CMA"
> 
> -> CONFIG_DMA_CMA won't be part of .config
> 
> 2. With no specification of CONFIG_CMA or CONFIG_DMA_CMA
> 
> Contiguous Memory Allocator (CMA) [Y/n/?] (NEW)
> DMA Contiguous Memory Allocator (DMA_CMA) [Y/n/?] (NEW)
> 
> 3. With "# CONFIG_CMA is not set" and "# CONFIG_DMA_CMA is not set"
> 
> -> CONFIG_DMA_CMA will be removed from .config
> 
> Note: drivers/remoteproc seems to be special; commit c51e882cd711
> ("remoteproc/davinci: Update Kconfig to depend on DMA_CMA") explains that
> there is a real dependency to DMA_CMA for it to work; leave that dependency
> in place and don't convert it to a soft dependency.

Hm, to me this sounds much like the reasoning for the etnaviv
dependency. There is no actual build dependency, as the allocations are
done through the DMA API, but for the allocations to succeed you most
likely want CMA to be enabled. But that's just an observation from the
outside, I have no real clue about the remoteproc drivers.

As far as the etnaviv changes are concerned:
Acked-by: Lucas Stach <l.stach at pengutronix.de>

> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: Maxime Ripard <mripard at kernel.org>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Joel Stanley <joel at jms.id.au>
> Cc: Andrew Jeffery <andrew at aj.id.au>
> Cc: Lucas Stach <l.stach at pengutronix.de>
> Cc: Russell King <linux+etnaviv at armlinux.org.uk>
> Cc: Christian Gmeiner <christian.gmeiner at gmail.com>
> Cc: Paul Cercueil <paul at crapouillou.net>
> Cc: Linus Walleij <linus.walleij at linaro.org>
> Cc: Christoph Hellwig <hch at lst.de>
> Cc: Marek Szyprowski <m.szyprowski at samsung.com>
> Cc: Robin Murphy <robin.murphy at arm.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Mike Rapoport <rppt at kernel.org>
> Cc: Arnd Bergmann <arnd at arndb.de>
> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie at samsung.com>
> Cc: Eric Anholt <eric at anholt.net>
> Cc: Michal Simek <michal.simek at xilinx.com>
> Cc: Masahiro Yamada <masahiroy at kernel.org>
> Cc: "Alexander A. Klimov" <grandmaster at al2klimov.de>
> Cc: Peter Collingbourne <pcc at google.com>
> Cc: Suman Anna <s-anna at ti.com>
> Cc: Jason Gunthorpe <jgg at ziepe.ca>
> Cc: dri-devel at lists.freedesktop.org
> Cc: linux-aspeed at lists.ozlabs.org
> Cc: linux-arm-kernel at lists.infradead.org
> Cc: etnaviv at lists.freedesktop.org
> Cc: linux-mips at vger.kernel.org
> Cc: linux-fbdev at vger.kernel.org
> Cc: iommu at lists.linux-foundation.org
> Signed-off-by: David Hildenbrand <david at redhat.com>
> ---
> 
> Let's see if this approach is better for soft dependencies (and if we
> actually have some hard dependencies in there). This is the follow-up
> of
>   https://lkml.kernel.org/r/20210408092011.52763-1-david@redhat.com
>   https://lkml.kernel.org/r/20210408100523.63356-1-david@redhat.com
> 
> I was wondering if it would make sense in some drivers to warn if either
> CONFIG_DMA_CMA is not available or if DRM_CMA has not been configured
> properly - just to give people a heads up that something might more likely
> go wrong; that would, however, be future work.
> 
> v2 -> v3:
> - Don't use "imply" but instead use a new WANT_DMA_CMA and make the default
>   of CMA and DMA_CMA depend on it.
> - Also adjust ingenic, mcde, tve200; these sound like soft dependencies as
>   well (although DMA_CMA is really desired)
> 
> v1 -> v2:
> - Fix DRM_CMA -> DMA_CMA
> 
> ---
>  drivers/gpu/drm/Kconfig         | 2 ++
>  drivers/gpu/drm/aspeed/Kconfig  | 2 --
>  drivers/gpu/drm/etnaviv/Kconfig | 3 +--
>  drivers/gpu/drm/ingenic/Kconfig | 1 -
>  drivers/gpu/drm/mcde/Kconfig    | 1 -
>  drivers/gpu/drm/tve200/Kconfig  | 1 -
>  drivers/video/fbdev/Kconfig     | 2 +-
>  kernel/dma/Kconfig              | 7 +++++++
>  mm/Kconfig                      | 1 +
>  9 files changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 85b79a7fee63..6f9989adfa93 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -201,12 +201,14 @@ config DRM_TTM_HELPER
>  config DRM_GEM_CMA_HELPER
>  	bool
>  	depends on DRM
> +	select WANT_DMA_CMA
>  	help
>  	  Choose this if you need the GEM CMA helper functions
>  
> 
> 
> 
>  config DRM_KMS_CMA_HELPER
>  	bool
>  	depends on DRM
> +	select WANT_DMA_CMA
>  	select DRM_GEM_CMA_HELPER
>  	help
>  	  Choose this if you need the KMS CMA helper functions
> diff --git a/drivers/gpu/drm/aspeed/Kconfig b/drivers/gpu/drm/aspeed/Kconfig
> index 5e95bcea43e9..e5ff33f85f21 100644
> --- a/drivers/gpu/drm/aspeed/Kconfig
> +++ b/drivers/gpu/drm/aspeed/Kconfig
> @@ -6,8 +6,6 @@ config DRM_ASPEED_GFX
>  	depends on MMU
>  	select DRM_KMS_HELPER
>  	select DRM_KMS_CMA_HELPER
> -	select DMA_CMA if HAVE_DMA_CONTIGUOUS
> -	select CMA if HAVE_DMA_CONTIGUOUS
>  	select MFD_SYSCON
>  	help
>  	  Chose this option if you have an ASPEED AST2500 SOC Display
> diff --git a/drivers/gpu/drm/etnaviv/Kconfig b/drivers/gpu/drm/etnaviv/Kconfig
> index faa7fc68b009..a3e7649b44a7 100644
> --- a/drivers/gpu/drm/etnaviv/Kconfig
> +++ b/drivers/gpu/drm/etnaviv/Kconfig
> @@ -9,8 +9,7 @@ config DRM_ETNAVIV
>  	select THERMAL if DRM_ETNAVIV_THERMAL
>  	select TMPFS
>  	select WANT_DEV_COREDUMP
> -	select CMA if HAVE_DMA_CONTIGUOUS
> -	select DMA_CMA if HAVE_DMA_CONTIGUOUS
> +	select WANT_DMA_CMA
>  	select DRM_SCHED
>  	help
>  	  DRM driver for Vivante GPUs.
> diff --git a/drivers/gpu/drm/ingenic/Kconfig b/drivers/gpu/drm/ingenic/Kconfig
> index 3b57f8be007c..156b11b7bbb8 100644
> --- a/drivers/gpu/drm/ingenic/Kconfig
> +++ b/drivers/gpu/drm/ingenic/Kconfig
> @@ -2,7 +2,6 @@ config DRM_INGENIC
>  	tristate "DRM Support for Ingenic SoCs"
>  	depends on MIPS || COMPILE_TEST
>  	depends on DRM
> -	depends on CMA
>  	depends on OF
>  	depends on COMMON_CLK
>  	select DRM_BRIDGE
> diff --git a/drivers/gpu/drm/mcde/Kconfig b/drivers/gpu/drm/mcde/Kconfig
> index 71c689b573c9..217d54c4babc 100644
> --- a/drivers/gpu/drm/mcde/Kconfig
> +++ b/drivers/gpu/drm/mcde/Kconfig
> @@ -1,7 +1,6 @@
>  config DRM_MCDE
>  	tristate "DRM Support for ST-Ericsson MCDE (Multichannel Display Engine)"
>  	depends on DRM
> -	depends on CMA
>  	depends on ARM || COMPILE_TEST
>  	depends on OF
>  	depends on COMMON_CLK
> diff --git a/drivers/gpu/drm/tve200/Kconfig b/drivers/gpu/drm/tve200/Kconfig
> index e2d163c74ed6..d04b7322c770 100644
> --- a/drivers/gpu/drm/tve200/Kconfig
> +++ b/drivers/gpu/drm/tve200/Kconfig
> @@ -2,7 +2,6 @@
>  config DRM_TVE200
>  	tristate "DRM Support for Faraday TV Encoder TVE200"
>  	depends on DRM
> -	depends on CMA
>  	depends on ARM || COMPILE_TEST
>  	depends on OF
>  	select DRM_BRIDGE
> diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
> index 4f02db65dede..e8acd4f77d41 100644
> --- a/drivers/video/fbdev/Kconfig
> +++ b/drivers/video/fbdev/Kconfig
> @@ -2186,7 +2186,7 @@ config FB_HYPERV
>  	select FB_CFB_COPYAREA
>  	select FB_CFB_IMAGEBLIT
>  	select FB_DEFERRED_IO
> -	select DMA_CMA if HAVE_DMA_CONTIGUOUS && CMA
> +	select WANT_DMA_CMA
>  	help
>  	  This framebuffer driver supports Microsoft Hyper-V Synthetic Video.
>  
> 
> 
> 
> diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> index 77b405508743..928f16d2461d 100644
> --- a/kernel/dma/Kconfig
> +++ b/kernel/dma/Kconfig
> @@ -103,8 +103,15 @@ config DMA_DIRECT_REMAP
>  	select DMA_REMAP
>  	select DMA_COHERENT_POOL
>  
> 
> 
> 
> +config WANT_DMA_CMA
> +	bool
> +	help
> +	  Drivers should "select" this option if they desire to use the
> +	  DMA_CMA mechanism.
> +
>  config DMA_CMA
>  	bool "DMA Contiguous Memory Allocator"
> +	default y if WANT_DMA_CMA
>  	depends on HAVE_DMA_CONTIGUOUS && CMA
>  	help
>  	  This enables the Contiguous Memory Allocator which allows drivers
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 24c045b24b95..169598ee56b1 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -485,6 +485,7 @@ config FRONTSWAP
>  
> 
> 
> 
>  config CMA
>  	bool "Contiguous Memory Allocator"
> +	default y if WANT_DMA_CMA
>  	depends on MMU
>  	select MIGRATION
>  	select MEMORY_ISOLATION