linux-kernel - Re: [PATCH 2/2] hwrng: mtk: Add driver for hardware random generator on MT7623 SoC

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Date:   Thu, 13 Apr 2017 14:09:45 +0530
From:   PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>
To:     sean.wang@...iatek.com
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Matt Mackall <mpm@...enic.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Corentin LABBE <clabbe.montjoie@...il.com>,
        Romain Perier <romain.perier@...e-electrons.com>,
        shannon.nelson@...cle.com, Wei Yongjun <weiyongjun1@...wei.com>,
        devicetree@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        keyhaede@...il.com
Subject: Re: [PATCH 2/2] hwrng: mtk: Add driver for hardware random generator
 on MT7623 SoC

Hi Sean,

Mostly looks good, have few minor comments.

On 13 April 2017 at 12:35,  <sean.wang@...iatek.com> wrote:
> +static bool mtk_rng_wait_ready(struct hwrng *rng, bool wait)
> +{
> +       struct mtk_rng *priv = to_mtk_rng(rng);
> +       int ready;
> +
> +       ready = readl(priv->base + RNG_CTRL) & RNG_READY;
> +       if (!ready && wait)
> +               readl_poll_timeout_atomic(priv->base + RNG_CTRL, ready,
> +                                         ready & RNG_READY, USEC_POLL,
> +                                         TIMEOUT_POLL);
> +       return !!ready;
> +}

Use readl_poll_timeout_atomic's return value or -EIO instead of
!!ready. This will simplify mtk_rng_read.

> +static int mtk_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> +{
> +       struct mtk_rng *priv = to_mtk_rng(rng);
> +       int retval = 0;
> +
> +       while (max >= sizeof(u32)) {
> +               if (!mtk_rng_wait_ready(rng, wait))
> +                       break;
> +
> +               *(u32 *)buf = readl(priv->base + RNG_DATA);
> +               retval += sizeof(u32);
> +               buf += sizeof(u32);
> +               max -= sizeof(u32);
> +       }
> +
> +       if (unlikely(wait && max))
> +               dev_warn(priv->dev, "timeout might be not properly set\n");

Is this really necessary? Better to choose proper timeout than
providing this warning message. In rare cases if the timeout could
occur due to some reason (may be a hardware fault) print appropriate
warning message.

> +       return retval || !wait ? retval : -EIO;
> +}

Set retavl to mtk_rng_wait_ready and return retval.

Regards,
Prasanna