Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Alexey Romanov <AVRomanov@sberdevices.ru>
To:     Martin Kaiser <lists@kaiser.cx>
CC:     "narmstrong@baylibre.com" <narmstrong@baylibre.com>,
        "neil.armstrong@linaro.org" <neil.armstrong@linaro.org>,
        "olivia@selenic.com" <olivia@selenic.com>,
        "herbert@gondor.apana.org.au" <herbert@gondor.apana.org.au>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "krzysztof.kozlowski+dt@linaro.org" 
        <krzysztof.kozlowski+dt@linaro.org>,
        "conor+dt@kernel.org" <conor+dt@kernel.org>,
        "khilman@baylibre.com" <khilman@baylibre.com>,
        "jbrunet@baylibre.com" <jbrunet@baylibre.com>,
        "martin.blumenstingl@googlemail.com" 
        <martin.blumenstingl@googlemail.com>,
        "f.fainelli@gmail.com" <f.fainelli@gmail.com>,
        "hkallweit1@gmail.com" <hkallweit1@gmail.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-amlogic@lists.infradead.org" 
        <linux-amlogic@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        kernel <kernel@sberdevices.ru>
Subject: Re: [PATCH v1 1/3] drivers: rng: add check status bit feature
Thread-Topic: [PATCH v1 1/3] drivers: rng: add check status bit feature
Thread-Index: AQHZvwIhgAdKkj3BKkSqydzslBnXI6/KtJqAgADHaIA=
Date:   Wed, 26 Jul 2023 07:52:43 +0000
Message-ID: <20230726075243.f37sjcurmog3eunh@cab-wsm-0029881>
References: <20230725141252.98848-1-avromanov@sberdevices.ru>
 <20230725141252.98848-2-avromanov@sberdevices.ru>
 <20230725195901.n2klvgz7outqaatk@viti.kaiser.cx>
In-Reply-To: <20230725195901.n2klvgz7outqaatk@viti.kaiser.cx>
Accept-Language: ru-RU, en-US
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-ID: <5A8C49A7B982AD4AA50B334FB89BE21D@sberdevices.ru>
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Precedence: bulk

Hi Martin,

On Tue, Jul 25, 2023 at 09:59:01PM +0200, Martin Kaiser wrote:
> Alexey Romanov (avromanov@sberdevices.ru) wrote:
>=20
> > For some Amlogic SOC's, mechanism to obtain random number
> > has been changed. For example, S4 now uses status bit waiting algo.
>=20
> > Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
> > ---
> >  drivers/char/hw_random/meson-rng.c | 77 ++++++++++++++++++++++++++++--
> >  1 file changed, 74 insertions(+), 3 deletions(-)
>=20
> > diff --git a/drivers/char/hw_random/meson-rng.c b/drivers/char/hw_rando=
m/meson-rng.c
> > index a4eb8e35f13d..c6d7349630a1 100644
> > --- a/drivers/char/hw_random/meson-rng.c
> > +++ b/drivers/char/hw_random/meson-rng.c
> > @@ -14,19 +14,65 @@
> >  #include <linux/of.h>
> >  #include <linux/clk.h>
>=20
> > -#define RNG_DATA 0x00
> > +struct meson_rng_priv {
> > +	bool check_status_bit;
> > +	unsigned int data_offset;
> > +	unsigned int cfg_offset;
> > +};
>=20
> >  struct meson_rng_data {
> >  	void __iomem *base;
> >  	struct hwrng rng;
> > +	struct device *dev;
> > +	const struct meson_rng_priv *priv;
> >  };
>=20
> > +#define RUN_BIT			0
> > +#define SEED_READY_STS_BIT	31
> > +#define RETRY_CNT		100
> > +
> > +static int meson_rng_wait_status(void __iomem *cfg_addr, int bit)
> > +{
> > +	u32 status;
> > +	u32 cnt =3D 0;
> > +
> > +	do {
> > +		status =3D readl_relaxed(cfg_addr) & BIT(bit);
> > +		cpu_relax();
> > +	} while (status && (cnt++ < RETRY_CNT));
> > +
>=20
> Could you use readl_relaxed_poll_timeout here instead of open coding the
> loop?

At first I also thought about this API. But later I came to the
conclusion that it is inappropriate here:

1. We can't call rng_read from an atomic context.
2. RNG for me looks like a very lightweight primitive to me that=20
should work quiclky.

But, now I looked again at the API and realized that we can use=20
readl_relaxed_poll_timeout_atomic() instead of
readl_relaxed_poll_timeout(). What do you think?

>=20
> > +	if (status)
> > +		return -EBUSY;
> > +
> > +	return 0;
> > +}
> > +
> >  static int meson_rng_read(struct hwrng *rng, void *buf, size_t max, bo=
ol wait)
> >  {
> >  	struct meson_rng_data *data =3D
> >  			container_of(rng, struct meson_rng_data, rng);
> > +	const struct meson_rng_priv *priv =3D data->priv;
> > +
> > +	if (priv->check_status_bit) {
> > +		void __iomem *cfg_addr =3D data->base + priv->cfg_offset;
> > +		int err;
> > +
> > +		writel_relaxed(readl_relaxed(cfg_addr) | BIT(SEED_READY_STS_BIT), cf=
g_addr);
>=20
> > -	*(u32 *)buf =3D readl_relaxed(data->base + RNG_DATA);
> > +		err =3D meson_rng_wait_status(cfg_addr, SEED_READY_STS_BIT);
> > +		if (err) {
> > +			dev_err(data->dev, "Seed isn't ready, try again\n");
> > +			return err;
> > +		}
> > +
> > +		err =3D meson_rng_wait_status(cfg_addr, RUN_BIT);
> > +		if (err) {
> > +			dev_err(data->dev, "Can't get random number, try again\n");
> > +			return err;
> > +		}
> > +	}
> > +
> > +	*(u32 *)buf =3D readl_relaxed(data->base + priv->data_offset);
>=20
> >  	return sizeof(u32);
> >  }
> > @@ -41,6 +87,10 @@ static int meson_rng_probe(struct platform_device *p=
dev)
> >  	if (!data)
> >  		return -ENOMEM;
>=20
> > +	data->priv =3D device_get_match_data(&pdev->dev);
> > +	if (!data->priv)
> > +		return -ENODEV;
> > +
> >  	data->base =3D devm_platform_ioremap_resource(pdev, 0);
> >  	if (IS_ERR(data->base))
> >  		return PTR_ERR(data->base);
> > @@ -53,11 +103,32 @@ static int meson_rng_probe(struct platform_device =
*pdev)
> >  	data->rng.name =3D pdev->name;
> >  	data->rng.read =3D meson_rng_read;
>=20
> > +	data->dev =3D &pdev->dev;
> > +
> >  	return devm_hwrng_register(dev, &data->rng);
> >  }
>=20
> > +static const struct meson_rng_priv meson_rng_priv =3D {
> > +	.check_status_bit =3D false,
> > +	.data_offset =3D 0x0,
> > +	.cfg_offset =3D 0x0,
> > +};
> > +
> > +static const struct meson_rng_priv meson_rng_priv_s4 =3D {
> > +	.check_status_bit =3D true,
> > +	.data_offset =3D 0x8,
> > +	.cfg_offset =3D 0x0,
> > +};
> > +
> >  static const struct of_device_id meson_rng_of_match[] =3D {
> > -	{ .compatible =3D "amlogic,meson-rng", },
> > +	{
> > +		.compatible =3D "amlogic,meson-rng",
> > +		.data =3D (void *)&meson_rng_priv,
> > +	},
> > +	{
> > +		.compatible =3D "amlogic,meson-rng-s4",
> > +		.data =3D (void *)&meson_rng_priv_s4,
> > +	},
> >  	{},
> >  };
> >  MODULE_DEVICE_TABLE(of, meson_rng_of_match);
> > --=20
> > 2.38.1
>=20

--=20
Thank you,
Alexey=