On Thu, Apr 8, 2021 at 12:29 PM David Hildenbrand david@redhat.com wrote:
On 08.04.21 12:20, Arnd Bergmann wrote:
On Thu, Apr 8, 2021 at 11:22 AM David Hildenbrand david@redhat.com wrote:
Random drivers should not override a user configuration of core knobs (e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect dependencies and manual overrides.
"This is similar to "select" as it enforces a lower limit on another symbol except that the "implied" symbol's value may still be set to n from a direct dependency or with a visible prompt."
Implying DRM_CMA should be sufficient, as that depends on CMA.
Note: If this is a real dependency, we should use "depends on DMA_CMA" instead - but I assume the driver can work without CMA just fine -- esp. when we wouldn't have HAVE_DMA_CONTIGUOUS right now.
'imply' is almost never the right solution, and it tends to cause more problems than it solves.
I thought that was the case with "select" :)
Yes, but that's a different set of problems
In particular, it does not prevent a configuration with 'DRM_CMA=m'
I assume you meant "DRM_CMA=n" ? DRM_CMA cannot be built as a module.
Ok, at least that makes it easier.
and 'DRMA_ASPEED_GFX=y', or any build failures from such a configuration.
I don't follow. "DRM_CMA=n" and 'DRMA_ASPEED_GFX=y' is supposed to work just fine (e.g., without HAVE_DMA_CONTIGUOUS) or what am I missing?
I thought you were trying to solve the problem where DRMA_ASPEED_GFX can optionally link against CMA but would fail to build when the CMA code is in a loadable module.
If the problem you are trying to solve is a different one, you need a different solution, not what I posted above.
If you want this kind of soft dependency, you need 'depends on DRM_CMA || !DRM_CMA'.
Seriously? I think the point of imply is "please enable if possible and not prevented by someone else".
That used to be the meaning, but it changed a few years ago. Now it means "when a used manually turns on this symbol, turn on the implied one as well, but let them turn it off again if they choose".
This is pretty much a NOP.
Your example looks more like a NOP - no? Or will it have the same effect?
The example I gave is only meaningful if both are tristate, which is not the case here as you explain.
It is a somewhat awkward way to say "prevent this symbol from being =y if the dependency is =m".
Arnd