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

[Rasmus Villemoes <ravi@prevas.dk>]

On Sun, May 25 2025, Tom Rini <trini@konsulko.com> wrote:

> On Sun, May 25, 2025 at 10:07:56PM +0200, Rasmus Villemoes wrote:
>> 
>> :( 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? 
>
> The answer is likely early 2000s GCC.
>
>> 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.
>
> It would be a good thing to experiment with now and maybe try for real
> in a near-future merge window.

So since it's declared per architecture I just tried with arm for now,
and this

diff --git a/arch/arm/include/asm/global_data.h b/arch/arm/include/asm/global_data.h
index 45401d5e3c8..f7a47204b7c 100644
--- a/arch/arm/include/asm/global_data.h
+++ b/arch/arm/include/asm/global_data.h
@@ -133,9 +133,9 @@ static inline gd_t *get_gd(void)
 #else
 
 #ifdef CONFIG_ARM64
-#define DECLARE_GLOBAL_DATA_PTR                register volatile gd_t *gd asm ("x18")
+#define DECLARE_GLOBAL_DATA_PTR                register gd_t *gd asm ("x18")
 #else
-#define DECLARE_GLOBAL_DATA_PTR                register volatile gd_t *gd asm ("r9")
+#define DECLARE_GLOBAL_DATA_PTR                register gd_t *gd asm ("r9")
 #endif
 #endif
 

builds, boots to linux, and passes our test suite on our
beagleboneblack, imx7 SabreSD, RPi 3, RPi 4, RPi-cm4, wandboard,
imx8mp-evk; i.e. a good mix of 32 and 64 bit arm.

Rasmus