On Thu, Jan 26, 2023, at 11:45, Geert Uytterhoeven wrote: > It is considered good practice to call cpu_relax() in busy loops, see > Documentation/process/volatile-considered-harmful.rst. This can not > only lower CPU power consumption or yield to a hyperthreaded twin > processor, but also allows an architecture to mitigate hardware issues > (e.g. ARM Erratum 754327 for Cortex-A9 prior to r2p0) in the > architecture-specific cpu_relax() implementation. > > As the iopoll helpers lack calls to cpu_relax(), people are sometimes > reluctant to use them, and may fall back to open-coded polling loops > (including cpu_relax() calls) instead. > > Fix this by adding calls to cpu_relax() to the iopoll helpers: > - For the non-atomic case, it is sufficient to call cpu_relax() in > case of a zero sleep-between-reads value, as a call to > usleep_range() is a safe barrier otherwise. > - For the atomic case, cpu_relax() must be called regardless of the > sleep-between-reads value, as there is no guarantee all > architecture-specific implementations of udelay() handle this. > > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx> Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
