Messages in this thread | | | Subject | Re: [PATCH v3] drivers: introduce and use WANT_DMA_CMA for soft dependencies on DMA_CMA | From | David Hildenbrand <> | Date | Fri, 9 Apr 2021 15:39:47 +0200 |
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On 09.04.21 15:35, Arnd Bergmann wrote: > On Fri, Apr 9, 2021 at 1:21 PM David Hildenbrand <david@redhat.com> wrote: >> >> 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. > > I don't think this dependency is fundamentally different from the others, > though davinci machines tend to have less memory than a lot of the > other machines, so it's more likely to fail without CMA. >
I was also unsure - and Lucas had similar thoughts. If you want, I can send a v4 also taking care of this.
Thanks!
> Regardless of this, > > Reviewed-by: Arnd Bergmann <arnd@arndb.de> >
-- Thanks,
David / dhildenb
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