[PATCH 0/4] list.h/treewide: get rid of no-op prefetch()
Rasmus Villemoes
ravi at prevas.dk
Sun May 25 22:07:56 CEST 2025
On Thu, May 22 2025, Tom Rini <trini at 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
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