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Message-ID: <20230726075243.f37sjcurmog3eunh@cab-wsm-0029881>
Date: Wed, 26 Jul 2023 07:52:43 +0000
From: Alexey Romanov <AVRomanov@...rdevices.ru>
To: Martin Kaiser <lists@...ser.cx>
CC: "narmstrong@...libre.com" <narmstrong@...libre.com>,
"neil.armstrong@...aro.org" <neil.armstrong@...aro.org>,
"olivia@...enic.com" <olivia@...enic.com>,
"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
"robh+dt@...nel.org" <robh+dt@...nel.org>,
"krzysztof.kozlowski+dt@...aro.org"
<krzysztof.kozlowski+dt@...aro.org>,
"conor+dt@...nel.org" <conor+dt@...nel.org>,
"khilman@...libre.com" <khilman@...libre.com>,
"jbrunet@...libre.com" <jbrunet@...libre.com>,
"martin.blumenstingl@...glemail.com"
<martin.blumenstingl@...glemail.com>,
"f.fainelli@...il.com" <f.fainelli@...il.com>,
"hkallweit1@...il.com" <hkallweit1@...il.com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-amlogic@...ts.infradead.org"
<linux-amlogic@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
kernel <kernel@...rdevices.ru>
Subject: Re: [PATCH v1 1/3] drivers: rng: add check status bit feature
Hi Martin,
On Tue, Jul 25, 2023 at 09:59:01PM +0200, Martin Kaiser wrote:
> Alexey Romanov (avromanov@...rdevices.ru) wrote:
>
> > For some Amlogic SOC's, mechanism to obtain random number
> > has been changed. For example, S4 now uses status bit waiting algo.
>
> > Signed-off-by: Alexey Romanov <avromanov@...rdevices.ru>
> > ---
> > drivers/char/hw_random/meson-rng.c | 77 ++++++++++++++++++++++++++++--
> > 1 file changed, 74 insertions(+), 3 deletions(-)
>
> > diff --git a/drivers/char/hw_random/meson-rng.c b/drivers/char/hw_random/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>
>
> > -#define RNG_DATA 0x00
> > +struct meson_rng_priv {
> > + bool check_status_bit;
> > + unsigned int data_offset;
> > + unsigned int cfg_offset;
> > +};
>
> > struct meson_rng_data {
> > void __iomem *base;
> > struct hwrng rng;
> > + struct device *dev;
> > + const struct meson_rng_priv *priv;
> > };
>
> > +#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 = 0;
> > +
> > + do {
> > + status = readl_relaxed(cfg_addr) & BIT(bit);
> > + cpu_relax();
> > + } while (status && (cnt++ < RETRY_CNT));
> > +
>
> 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
should work quiclky.
But, now I looked again at the API and realized that we can use
readl_relaxed_poll_timeout_atomic() instead of
readl_relaxed_poll_timeout(). What do you think?
>
> > + if (status)
> > + return -EBUSY;
> > +
> > + return 0;
> > +}
> > +
> > static int meson_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> > {
> > struct meson_rng_data *data =
> > container_of(rng, struct meson_rng_data, rng);
> > + const struct meson_rng_priv *priv = data->priv;
> > +
> > + if (priv->check_status_bit) {
> > + void __iomem *cfg_addr = data->base + priv->cfg_offset;
> > + int err;
> > +
> > + writel_relaxed(readl_relaxed(cfg_addr) | BIT(SEED_READY_STS_BIT), cfg_addr);
>
> > - *(u32 *)buf = readl_relaxed(data->base + RNG_DATA);
> > + err = 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 = 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 = readl_relaxed(data->base + priv->data_offset);
>
> > return sizeof(u32);
> > }
> > @@ -41,6 +87,10 @@ static int meson_rng_probe(struct platform_device *pdev)
> > if (!data)
> > return -ENOMEM;
>
> > + data->priv = device_get_match_data(&pdev->dev);
> > + if (!data->priv)
> > + return -ENODEV;
> > +
> > data->base = 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 = pdev->name;
> > data->rng.read = meson_rng_read;
>
> > + data->dev = &pdev->dev;
> > +
> > return devm_hwrng_register(dev, &data->rng);
> > }
>
> > +static const struct meson_rng_priv meson_rng_priv = {
> > + .check_status_bit = false,
> > + .data_offset = 0x0,
> > + .cfg_offset = 0x0,
> > +};
> > +
> > +static const struct meson_rng_priv meson_rng_priv_s4 = {
> > + .check_status_bit = true,
> > + .data_offset = 0x8,
> > + .cfg_offset = 0x0,
> > +};
> > +
> > static const struct of_device_id meson_rng_of_match[] = {
> > - { .compatible = "amlogic,meson-rng", },
> > + {
> > + .compatible = "amlogic,meson-rng",
> > + .data = (void *)&meson_rng_priv,
> > + },
> > + {
> > + .compatible = "amlogic,meson-rng-s4",
> > + .data = (void *)&meson_rng_priv_s4,
> > + },
> > {},
> > };
> > MODULE_DEVICE_TABLE(of, meson_rng_of_match);
> > --
> > 2.38.1
>
--
Thank you,
Alexey
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