cpu/nrf52 i2c: Always buffer writes #20298
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The underlying peripheral can only read from RAM. This uses the existing infrastructure (already needed to work around the lack of a hardware support for I2C_NOSTART) to unconditionally copy any to-be-sent data into RAM.
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Platform: ARM
chrysn
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Type: bug
benpicco
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Jan 25, 2024
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benpicco
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The branch name is quite confusing :D |
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If that's confusing than please don't look at #20299, which is |
kaspar030
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Jan 25, 2024
| @@ -331,6 +339,31 @@ int i2c_read_regs(i2c_t dev, uint16_t addr, uint16_t reg, | |||
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| int i2c_write_bytes(i2c_t dev, uint16_t addr, const void *data, size_t len, | |||
| uint8_t flags) | |||
| { | |||
| if ((unsigned int)data >= CPU_RAM_BASE && (unsigned int)data < CPU_RAM_BASE + CPU_RAM_SIZE) { | |||
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This is done a bit simpler for spi:
Would that work here, too? Is that too relaxed for SPI?
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... embassy-nrf does this:
const SRAM_LOWER: usize = 0x2000_0000;
const SRAM_UPPER: usize = 0x3000_0000;
ptr >= SRAM_LOWER && (ptr + len * core::mem::size_of::<T>()) < SRAM_UPPER
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The SPI version is probably good enough, we could unify. The embassy version is IMO excessive, as the slice is a single object, and objects don't span memmapping areas.
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Contribution description
The underlying peripheral can only read from RAM. This uses the existing infrastructure (already needed to work around the lack of a hardware support for I2C_NOSTART) to unconditionally copy any to-be-sent data into RAM.
There is certainly an alternative where we determine at runtime whether the data is in RAM or in ROM and only lock and copy if it's in ROM, but I'd only do that if we have concrete benchmarks that show that this is an issue.
Testing procedure