On 09.04.21 15:35, Arnd Bergmann wrote:
On Fri, Apr 9, 2021 at 1:21 PM David Hildenbrand <david@xxxxxxxxxx> 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@xxxxxxxx>
-- Thanks, David / dhildenb
