benmccrea commented on a change in pull request #2392:
URL: https://github.com/apache/mynewt-core/pull/2392#discussion_r506617502
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File path: hw/drivers/crypto/crypto_da1469x/src/crypto_da1469x.c
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@@ -73,7 +74,10 @@ do_dma_key_tx(const void *key, uint16_t keylen)
da1469x_otp_set_mode(OTPC_MODE_READ);
/* securely DMA hardware key from secret storage to QSPI decrypt engine */
- dma_regs->DMA_REQ_MUX_REG |= 0xf000;
+ OS_ENTER_CRITICAL(sr);
+ /* Use the secure channel #7 */
+ MCU_DMA_SET_MUX(7, MCU_DMA_PERIPH_NONE);
Review comment:
@nkaje I don't believe this will work properly. I think the
MCU_DMA_SET_MUX macro expects to work on channel-pair requests, where the lower
channel index of the pair is passed as cidx.
DMA_REQ_MUX_REG is a 16-bit register. If you pass cidx=7 to this macro, the
resulting bit mask and bit set values will be shifted beyond bit 15 in the
register:
Example: cidx=7, periph=MCU_DMA_PERIPH_NONE=0xf
(_periph) << ((_cidx) * 2) --> left-shift 0xf by 14 bits =
b111100000000000000 = 0x3c000
I think the `MCU_DMA_SET_MUX` macro was intended to be used privately in
da1469x_dma.c by `da1469x_dma_acquire_single()` and
`da1469x_dma_acquire_periph()`.
Take a look at this code in `da1469x_dma_acquire_single()`:
```
/*
* DMA_REQ_MUX_REG applies only to channels < 8
*/
if (cidx < 8) {
MCU_DMA_SET_MUX(cidx, MCU_DMA_PERIPH_NONE);
}
```
Note that this code will not work properly for odd-numbered channels. Even
though it is a single channel request, the lower channel # of a channel pair
must be passed for it to work properly.
I think we need to do both of the following to really fix this issue:
1. Fix `da1469x_dma_acquire_single()` so it properly works for both even and
odd single-channel requests.
2. Use `da1469x_dma_acquire_single()` and `da1469x_dma_release_channel()` in
the crypto code for channel 7, so that the DMA driver can function properly
when channel 7 is in use.
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