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SubjectRe: [PATCH v7 11/17] openrisc: account for 0 starting value in random_get_entropy()
Hi Stafford,

On Sun, May 01, 2022 at 07:11:37AM +0900, Stafford Horne wrote:

> I was thinking about this, the reason the tick timer is returing 0 is because
> the timer is not started. It's getting initialized right after the random
> number generator.
>
> A patch like this helps to startup the timer during intial startup, but I am not
> sure its the best thing:
>
> diff --git a/arch/openrisc/kernel/head.S b/arch/openrisc/kernel/head.S
> index 15f1b38dfe03..a9b3b5614e13 100644
> --- a/arch/openrisc/kernel/head.S
> +++ b/arch/openrisc/kernel/head.S
> @@ -521,6 +521,9 @@ _start:
> l.ori r3,r0,0x1
> l.mtspr r0,r3,SPR_SR
>
> + l.movhi r3,hi(SPR_TTMR_CR)
> + l.mtspr r0,r3,SPR_TTMR
> +
> CLEAR_GPR(r1)
> CLEAR_GPR(r2)
> CLEAR_GPR(r3)

Yea, great, I was thinking about doing it in assembly earlier in boot
too, but didn't know how you'd feel about that. I like this better.

The reason I think this is a good approach is that it means the cycle
counter includes some information about how long startup takes from the
earliest stages -- which could involve probing various devices or
strange things. So enabling the timer in head.S seems good to me.

> But I wonder:
> - Why don't any other architectures have similar issues.
> - Is there any more correct place to do an early timer kick off.

I think most other archs (like, say, x86) have their cycle counter
enabled by default at boot time. I was surprised to see that the or1k
risc cycle counter comes disabled by default actually.

I'll send a v9 incorporating your suggested assembly change.

Jason

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