Re: [RFC PATCH 00/10] Add Fujitsu A64FX soc entry/hardware barrier driver
From: Mark Rutland <mark.rutland@arm.com>
Date: 2021-01-08 15:53:51
On Fri, Jan 08, 2021 at 03:23:23PM +0100, Arnd Bergmann wrote:
On Fri, Jan 8, 2021 at 1:54 PM Mark Rutland [off-list ref] wrote:quoted
As a general rule, we avoid the use of IMPLEMENTATION DEFINED features in Linux, as they pose a number of correctness/safety challenges and come with a potentially significan long term maintenance burden that is generally not justified by the features themselves. For example, such features are not usable under virtualization (where a hypervisor may set HCR_EL2.TIDCP, or fail to context-switch state that it is unaware of).I am somewhat less concerned about the feature being implementation defined than I am about adding a custom user interface for one platform.
I completely agree that adding a custom interface that's platform specific is undesireable.
In the end, anything outside of the CPU core that ends up in a SoC is implementation defined, and this is usually not a problem as long as we have an abstraction in the kernel that hides the details from the user, and the system is still functional if the implementation is turned off for whatever reason.
I think that peripherals and other bits out in the SoC are quite different to things built into the CPU, where there's inevitably most significant and subtle interactions with the architecture, and can be so closely coupled as to not have a good point to apply abstraction. We have common ways of abstracting storage devices, but the same is not as true for userspace instructions. Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel