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

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Date:   Mon, 9 Jan 2023 02:58:14 +0000
From:   JiaJie Ho <jiajie.ho@...rfivetech.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
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



> -----Original Message-----
> From: Herbert Xu <herbert@...dor.apana.org.au>
> Sent: 6 January, 2023 4:39 PM
> 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; devicetree@...r.kernel.org; linux-
> kernel@...r.kernel.org; linux-riscv@...ts.infradead.org
> Subject: Re: [PATCH v2 2/3] hwrng: starfive - Add TRNG driver for StarFive
> SoC
> 
> On Wed, Dec 28, 2022 at 03:11:02PM +0800, Jia Jie Ho wrote:
> > +static int starfive_trng_read(struct hwrng *rng, void *buf, size_t
> > +max, bool wait)
> 
> You should respect the wait argument and not do polling/sleeping if it is false.
> 

Hi Herbert, 

My trng device requires sending a generate new number cmd before each read.
It then only populates the data registers with new random number and raise an interrupt when ready.
If user choose to not wait, they will always get stale bits. 
Is it okay to always return error if wait=false ?

Thanks
Jia Jie