gpio: mcp23s08: use edge-triggered interrupts - #48
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This prevents deadlock on startup when INT line is held low during startup of mcp23s08 module. Interrupt is cleared by talking to all mcp23s08 devices sharing same INT line. On startup, the devieces are probed one by one. The first device probed initialize IRQ handler on INT line. Since the other deviecs sharing INT line are not probed at this point, interrupt cannot be cleared. Continuos interrupt handling, in turn, will prevent other devices to be probed by blocking i2c bus. Edge triggered interrupts are triggered only once, thus preventing the aforementioned scenario. s in this case interrupt can't be cleared
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Jun 9, 2025
… prevent wrong idmap generation commit 363cd2b upstream. The PTE_MAYBE_NG macro sets the nG page table bit according to the value of "arm64_use_ng_mappings". This variable is currently placed in the .bss section. create_init_idmap() is called before the .bss section initialisation which is done in early_map_kernel(). Therefore, data/test_prot in create_init_idmap() could be set incorrectly through the PAGE_KERNEL -> PROT_DEFAULT -> PTE_MAYBE_NG macros. # llvm-objdump-21 --syms vmlinux-gcc | grep arm64_use_ng_mappings ffff800082f242a8 g O .bss 0000000000000001 arm64_use_ng_mappings The create_init_idmap() function disassembly compiled with llvm-21: // create_init_idmap() ffff80008255c058: d10103ff sub sp, sp, #0x40 ffff80008255c05c: a9017bfd stp x29, x30, [sp, #0x10] ffff80008255c060: a90257f6 stp x22, x21, [sp, #0x20] ffff80008255c064: a9034ff4 stp x20, x19, [sp, #0x30] ffff80008255c068: 910043fd add x29, sp, #0x10 ffff80008255c06c: 90003fc8 adrp x8, 0xffff800082d54000 ffff80008255c070: d280e06a mov x10, #0x703 // =1795 ffff80008255c074: 91400409 add x9, x0, #0x1, lsl #12 // =0x1000 ffff80008255c078: 394a4108 ldrb w8, [x8, #0x290] ------------- (1) ffff80008255c07c: f2e00d0a movk x10, #0x68, lsl #48 ffff80008255c080: f90007e9 str x9, [sp, #0x8] ffff80008255c084: aa0103f3 mov x19, x1 ffff80008255c088: aa0003f4 mov x20, x0 ffff80008255c08c: 14000000 b 0xffff80008255c08c <__pi_create_init_idmap+0x34> ffff80008255c090: aa082d56 orr x22, x10, x8, lsl #11 -------- (2) Note (1) is loading the arm64_use_ng_mappings value in w8 and (2) is set the text or data prot with the w8 value to set PTE_NG bit. If the .bss section isn't initialized, x8 could include a garbage value and generate an incorrect mapping. Annotate arm64_use_ng_mappings as __read_mostly so that it is placed in the .data section. Fixes: 84b04d3 ("arm64: kernel: Create initial ID map from C code") Cc: stable@vger.kernel.org # 6.9.x Tested-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com> Link: https://lore.kernel.org/r/20250502180412.3774883-1-yeoreum.yun@arm.com [catalin.marinas@arm.com: use __read_mostly instead of __ro_after_init] [catalin.marinas@arm.com: slight tweaking of the code comment] Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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This prevents deadlock on startup when INT line is held low during
startup of mcp23s08 module. Interrupt is cleared by talking to all
mcp23s08 devices sharing same INT line. On startup, the devieces
are probed one by one. The first device probed initialize IRQ handler
on INT line. Since the other deviecs sharing INT line are not probed
at this point, interrupt cannot be cleared.
Continuos interrupt handling, in turn, will prevent other devices to
be probed by blocking i2c bus.
Edge triggered interrupts are triggered only once, thus preventing the
aforementioned scenario.
s in this case interrupt can't be cleared