Re: [PATCH v2] spi: bcm2835: Enable shared interrupt support

[Lukas Wunner <lukas@xxxxxxxxx>]

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