On 2021-03-19 16:42, Mark Brown wrote:
On Thu, Mar 18, 2021 at 12:25:26PM +0000, Marc Zyngier wrote:
A common pattern is to conditionally update ZCR_ELx in order
to avoid the "self-synchronizing" effect that writing to this
register has.
Let's provide an accessor that does exactly this.
Reviewed-by: Mark Brown <broonie@xxxxxxxxxx>
+#define sve_cond_update_zcr_vq(val, reg) \
+ do { \
+ u64 __zcr = read_sysreg_s((reg)); \
+ u64 __new = __zcr & ~ZCR_ELx_LEN_MASK; \
+ __new |= (val) & ZCR_ELx_LEN_MASK; \
+ if (__zcr != __new) \
+ write_sysreg_s(__new, (reg)); \
+ } while (0)
+
Do compilers actually do much better with this than with a static
inline like the other functions in this header? Seems like something
they should be figuring out.
It's not about performance or anything of the sort: in most cases
where we end-up using this, it is on the back of an exception.
So performance is the least of our worries.
However, the "reg" parameter to read/write_sysreg_s() cannot
be a variable, because it is directly fed to the assembler.
If you want to use functions, you need to specialise them per
register. At this point, I'm pretty happy with a #define.
M.
--
Jazz is not dead. It just smells funny...
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