On Mon, Jun 08, 2020 at 12:11:11PM +0100, Robin Murphy wrote: > And all in code that has at least one obvious inefficiency left on > the table either way. Care to submit a patch to overcome that inefficiency? > This thread truly epitomises Knuth's "premature optimisation" quote... ;) The thread came about because it can be determined at compile time whether the interrupt is going to be shared: On the BCM2835 (Raspberry Pi 1), CONFIG_ARCH_MULTI_V6 is set and this SoC doesn't have multiple bcm2835-spi instances, so no shared interrupt. The question is how to discern BCM2836/BCM2837 (Raspberry Pi 2/3), which do not have multiple instances, and BCM2711 (Raspberry Pi 4) which does. The Raspberry Pi Foundation compiles BCM2711 kernels with CONFIG_ARM_LPAE=y, but Florian considered that kludgy as a discriminator and opted for runtime-detection via the compatible string instead. If you've got a better idea please come forward. Is "optimize shared IRQ support away if IS_ENABLED(CONFIG_ARCH_MULTI_V6), else leave it in" the best we can do? Thanks, Lukas
