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[86.9.19.6]) by smtp.gmail.com with ESMTPSA id u26sm18054666wrd.87.2019.10.14.05.27.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Oct 2019 05:27:34 -0700 (PDT) Date: Mon, 14 Oct 2019 13:27:32 +0100 From: Daniel Thompson To: Sumit Garg Cc: linux-crypto@vger.kernel.org, dsaxena@plexity.net, herbert@gondor.apana.org.au, mpm@selenic.com, romain.perier@free-electrons.com, arnd@arndb.de, gregkh@linuxfoundation.org, ralph.siemsen@linaro.org, milan.stevanovic@se.com, ryan.harkin@linaro.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] hwrng: omap - Fix RNG wait loop timeout Message-ID: <20191014122732.d6ow5tbko5xdwd7g@holly.lan> References: <1571054565-6991-1-git-send-email-sumit.garg@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1571054565-6991-1-git-send-email-sumit.garg@linaro.org> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 14, 2019 at 05:32:45PM +0530, Sumit Garg wrote: > Existing RNG data read timeout is 200us but it doesn't cover EIP76 RNG > data rate which takes approx. 700us to produce 16 bytes of output data > as per testing results. So configure the timeout as 1000us to also take > account of lack of udelay()'s reliability. What "lack of udelay()'s reliability" are you concerned about? Daniel. > > Fixes: 383212425c92 ("hwrng: omap - Add device variant for SafeXcel IP-76 found in Armada 8K") > Cc: > Signed-off-by: Sumit Garg > --- > drivers/char/hw_random/omap-rng.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/drivers/char/hw_random/omap-rng.c b/drivers/char/hw_random/omap-rng.c > index b27f396..e329f82 100644 > --- a/drivers/char/hw_random/omap-rng.c > +++ b/drivers/char/hw_random/omap-rng.c > @@ -66,6 +66,13 @@ > #define OMAP4_RNG_OUTPUT_SIZE 0x8 > #define EIP76_RNG_OUTPUT_SIZE 0x10 > > +/* > + * EIP76 RNG takes approx. 700us to produce 16 bytes of output data > + * as per testing results. And to account for the lack of udelay()'s > + * reliability, we keep the timeout as 1000us. > + */ > +#define RNG_DATA_FILL_TIMEOUT 100 > + > enum { > RNG_OUTPUT_0_REG = 0, > RNG_OUTPUT_1_REG, > @@ -176,7 +183,7 @@ static int omap_rng_do_read(struct hwrng *rng, void *data, size_t max, > if (max < priv->pdata->data_size) > return 0; > > - for (i = 0; i < 20; i++) { > + for (i = 0; i < RNG_DATA_FILL_TIMEOUT; i++) { > present = priv->pdata->data_present(priv); > if (present || !wait) > break; > -- > 2.7.4 >