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Pull up following revision(s) (requested by gutteridge in ticket #256): 

sys/arch/mips/cavium/dev/octeon_rnm.c: revision 1.16 (patch)

octrnm(4): Raise delay on startup.

According to CN50XX-HRM-V0.99E and CN78XX-HM-0.99E:
    The entropy is provided by the jitter of 125 of 128 free-running
    oscillators XORed into a 128-bit LFSR.  The LFSR accumulates entropy
    over 81 cycles, after which it is fed into a SHA-1 engine.
    [...]
    The SHA-1 engine runs once every 81 cycles.
    [...]
    The hardware produces new 64-bit random number every 81 cycles.

The last sentence means that we only need to wait 81 cycles _between_
consecutive SHA-1 outputs (which isn't relevant anyway because we
reconfigure it into raw mode later), but the first two quotes might
mean that we need to wait 81+81 cycles for the _first_ output to be
produced on boot when running the self-test.

Now, in this case, the self-test is run with the LFSR unhooked, by
clearing the RNM_CTL_STATUS[ENT_EN] bit, so that SHA-1 is computed
from a known input -- this is really just paranoia to make sure that
_some_ functions of the device (which is conjured out of thin air at
a fixed virtual address, with no firmware bindings to guide us)
behave as we expect.

And it's not clear if it really does take 81+81 cycles for the first
SHA-1 output to appear when the LFSR isn't feeding into it anyway.

But experimentally, delay of 81+81 cycles seems to work whereas a
delay of only 81 cycles crashes.
PR kern/57280
This commit is contained in:
martin 2023-07-30 11:41:48 +00:00
parent 7f27873a80
commit 7a9ccf5a97
1 changed files with 5 additions and 4 deletions
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9
sys/arch/mips/cavium/dev/octeon_rnm.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: octeon_rnm.c,v 1.2.4.2 2020/05/19 17:39:04 martin Exp $ */
/* $NetBSD: octeon_rnm.c,v 1.2.4.3 2023/07/30 11:41:48 martin Exp $ */
/*
* Copyright (c) 2007 Internet Initiative Japan, Inc.
@ -99,7 +99,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: octeon_rnm.c,v 1.2.4.2 2020/05/19 17:39:04 martin Exp $");
__KERNEL_RCSID(0, "$NetBSD: octeon_rnm.c,v 1.2.4.3 2023/07/30 11:41:48 martin Exp $");
#include <sys/param.h>
#include <sys/device.h>
@ -118,7 +118,8 @@ __KERNEL_RCSID(0, "$NetBSD: octeon_rnm.c,v 1.2.4.2 2020/05/19 17:39:04 martin Ex
//#define OCTEON_RNM_DEBUG
#define ENT_DELAY_CLOCK 8 /* cycles for each 64-bit RO sample batch */
#define RNG_DELAY_CLOCK 81 /* cycles for each SHA-1 output */
#define LFSR_DELAY_CLOCK 81 /* cycles to fill LFSR buffer */
#define SHA1_DELAY_CLOCK 81 /* cycles to compute SHA-1 output */
#define NROGROUPS 16
#define RNG_FIFO_WORDS (512/sizeof(uint64_t))
@ -195,7 +196,7 @@ octeon_rnm_attach(device_t parent, device_t self, void *aux)
*/
octeon_rnm_reset(sc);
octeon_rnm_conditioned_deterministic(sc);
octeon_rnm_delay(RNG_DELAY_CLOCK*1);
octeon_rnm_delay(LFSR_DELAY_CLOCK + SHA1_DELAY_CLOCK);
sample = octeon_rnm_load(sc);
if (sample != expected)
aprint_error_dev(self, "self-test: read %016"PRIx64","