linux-kernel - Re: [PATCH v2 2/3] hwrng: starfive - Add TRNG driver for StarFive SoC

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Message-ID: <Y7uRVNvplGjrZxa4@gondor.apana.org.au>
Date:   Mon, 9 Jan 2023 12:00:20 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     JiaJie Ho <jiajie.ho@...rfivetech.com>
Cc:     Olivia Mackall <olivia@...enic.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Emil Renner Berthing <kernel@...il.dk>,
        Conor Dooley <conor.dooley@...rochip.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v2 2/3] hwrng: starfive - Add TRNG driver for StarFive SoC

On Mon, Jan 09, 2023 at 03:41:14AM +0000, JiaJie Ho wrote:
>
> The average wait time is around 20 microseconds.
> I measured from writel cmd to wait_for_completion done.

Do you know of an upper bound? E.g., if we limit it to 40us how
many requests would fail on average?

Having a maximum delay of 40us would be OK with wait == 0.  So
you could implement it in a way such that if the wait time exceeded
40us then you return if wait == 0, otherwise you can wait longer.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt