Re: [PATCH 0/4] list.h/treewide: get rid of no-op prefetch()

[Rasmus Villemoes <ravi@prevas.dk>]

On Thu, May 22 2025, Tom Rini <trini@konsulko.com> wrote:

> On Wed, May 07, 2025 at 02:12:42PM +0200, Rasmus Villemoes wrote:
>
>> While looking through list.h, I saw that the regular list_* helpers
>> (and one of the hlist_* ones) still contain the prefetch() that was
>> removed in linux 14 years ago. It doesn't do anything, but makes the
>> macros harder to read, so get rid of it, and the fallback, no-op
>> definition that they relied on. That requires removing a few uses
>> outside list.h as well.
>> 
>> checkpatch warns about some whitespace issues in list.h, but as I've
>> copied whole kerneldoc+#define blocks directly from the linux kernel,
>> I think it's better to just accept that so that we don't introduce
>> needless diffs. The "macro argument reuse" arguments should also be
>> ignored, as e.g. the "member" arguments are obviously always just bare
>> identifiers, and the "pos" arguments must be assigned to multiple
>> times.
>> 
>> Rasmus Villemoes (4):
>>   linux/list.h: drop use of prefetch()
>>   treewide: drop no-op prefetch() calls
>>   mips: drop unused prefetch code and logic
>>   linux/list.h: drop fallback definition of prefetch()
>> 
>>  arch/mips/include/asm/processor.h |  16 -----
>>  drivers/net/mvpp2.c               |   1 -
>>  drivers/net/octeontx/nicvf_main.c |   2 -
>>  drivers/usb/gadget/at91_udc.c     |   1 -
>>  drivers/usb/musb-new/musb_core.c  |   2 -
>>  include/linux/list.h              | 104 +++++++++++++++++-------------
>>  6 files changed, 59 insertions(+), 67 deletions(-)
>
> Unfortunately this leads to build problems on lots of platforms:
> https://source.denx.de/u-boot/u-boot/-/jobs/1141951

:( so we've been relying on that prefetch() laundering away the
volatile.

Which really begs the question: Why, exactly, is it that gd even has
that volatile qualifier in the first place? 

I'm 98% certain that we could drop that and get better code generation
and avoid a ton of places where we cast away that volatile which
shouldn't really be there anyway.

Rasmus