> -----Original Message----- > From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> > Sent: 9 January, 2023 12:00 PM > To: JiaJie Ho <jiajie.ho@xxxxxxxxxxxxxxxx> > Cc: Olivia Mackall <olivia@xxxxxxxxxxx>; Rob Herring <robh+dt@xxxxxxxxxx>; > Krzysztof Kozlowski <krzysztof.kozlowski+dt@xxxxxxxxxx>; Emil Renner > Berthing <kernel@xxxxxxxx>; Conor Dooley <conor.dooley@xxxxxxxxxxxxx>; > linux-crypto@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx; linux-riscv@xxxxxxxxxxxxxxxxxxx > 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? > I don't have the upper bound. I ran the rngtest with 1000 blocks, none of the wait time exceeded 30us. > 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. > I'll do this then. Thanks Jia Jie
