Date: Fri, 10 May 2024 14:31:41 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Borislav Petkov <bp@...en8.de>
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Subject: Re: [RFC PATCH v8 01/10] ras: scrub: Add scrub subsystem


> How hard is that "jump through hoops" thing anyway?

I'd conservatively estimate 500 lines of duplicated code from the CXL
subsystem just to handle the setup and discovery of the mailbox, plus
all the checks needed to establish the device is in a state to reply.
Also locking or module load ordering constraints because we need
to ensure mutual exclusion on that mailbox between this module and the CXL
core. So it would approximately triple the size of this driver to
check for CXL scrub support. Not to mention hotplug - which could
possibly be solved with appropriate udev rules to try loading this again
whenever a CXL memory device gets plugged in.

Alternative would be to make this ras class driver dependent on the CXL
driver stack running first. Thus if you wanted RAS2 ACPI table support, you'd
need to load a whole bunch of CXL stuff.

Add another similar driver in future and we get another few 100 lines of code
or another dependency. To me those numbers make it unsustainable.

> 
> You mean it should load so that when booting an allmodconfig kernel there are not enough modules which are loading so lemme load one more. And then I need to go and rmmod them all before I need to do localmodconfig and build a tailored kernel for the machine.
> 
> Or is there some other reason to load silly modules, use up resources for no good reason whatsoever and bloat the machine?

As Dan, Shiju and I observed (and Shiju tested to be sure we weren't
getting it wrong), normal setups including your allmodconfig
build would not even load the driver.  What are we missing?

Jonathan

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