drivers: udc: mcux_ehci: rework control transfer handling#3
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allocate control buffers in stack Signed-off-by: Mark Wang <yichang.wang@nxp.com>
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1. Mostly complete. Supports MPU, userspace, PSPLIM-based stack guards, and FPU/DSP features. ARMv8-M secure mode "should" work but I don't know how to test it. 2. Designed with an eye to uncompromising/best-in-industry cooperative context switch performance. No PendSV exception nor hardware stacking/unstacking, just a traditional "musical chairs" switch. Context gets saved on process stacks only instead of split between there and the thread struct. No branches in the core integer switch code (and just one in the FPU bits that can't be avoided). 3. Minimal assembly use; arch_switch() itself is ALWAYS_INLINE, there is an assembly stub for exception exit, and that's it beyond one/two instruction inlines elsewhere. 4. Selectable at build time, interoperable with existing code. Just use the pre-existing CONFIG_USE_SWITCH=y flag to enable it. Or turn it off to evade regressions as this stabilizes. 5. Exception/interrupt returns in the common case need only a single C function to be called at the tail, and then return naturally. Effectively "all interrupts are direct now". This isn't a benefit currently because the existing stubs haven't been removed (see #4), but in the long term we can look at exploiting this. The boilerplate previously required is now (mostly) empty. 6. No support for ARMv6 (Cortex M0 et. al.) thumb code. The expanded instruction encodings in ARMv7 are a big (big) win, so the older cores really need a separate port to avoid impacting newer hardware. Thankfully there isn't that much code to port (see #3), so this should be doable. Signed-off-by: Andy Ross <andyross@google.com>
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allocate control buffers in stack