Re: [PATCH v1 2/2] hwrng: npcm: add NPCM RNG driver

[Tomer Maimon <tmaimon77@gmail.com>]

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Hi Daniel,

appreciate your comments and sorry for the late reply

On Thu, 29 Aug 2019 at 13:47, Daniel Thompson <daniel.thompson@linaro.org>
wrote:

> On Wed, Aug 28, 2019 at 07:26:17PM +0300, Tomer Maimon wrote:
> > Add Nuvoton NPCM BMC Random Number Generator(RNG) driver.
> >
> > Signed-off-by: Tomer Maimon <tmaimon77@gmail.com>
> > ---
> >  drivers/char/hw_random/Kconfig    |  13 ++
> >  drivers/char/hw_random/Makefile   |   1 +
> >  drivers/char/hw_random/npcm-rng.c | 207 ++++++++++++++++++++++++++++++
> >  3 files changed, 221 insertions(+)
> >  create mode 100644 drivers/char/hw_random/npcm-rng.c
> >
> > diff --git a/drivers/char/hw_random/npcm-rng.c
> b/drivers/char/hw_random/npcm-rng.c
> > new file mode 100644
> > index 000000000000..5b4b1b6cb362
> > --- /dev/null
> > +++ b/drivers/char/hw_random/npcm-rng.c
> > @@ -0,0 +1,207 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +// Copyright (c) 2019 Nuvoton Technology corporation.
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/io.h>
> > +#include <linux/iopoll.h>
> > +#include <linux/init.h>
> > +#include <linux/random.h>
> > +#include <linux/err.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/hw_random.h>
> > +#include <linux/delay.h>
> > +#include <linux/of_irq.h>
> > +#include <linux/pm_runtime.h>
> > +
> > +#define NPCM_RNGCS_REG               0x00    /* Control and status
> register */
> > +#define NPCM_RNGD_REG                0x04    /* Data register */
> > +#define NPCM_RNGMODE_REG     0x08    /* Mode register */
> > +
> > +#define NPCM_RNG_CLK_SET_25MHZ       GENMASK(4, 3) /* 20-25 MHz */
> > +#define NPCM_RNG_DATA_VALID  BIT(1)
> > +#define NPCM_RNG_ENABLE              BIT(0)
> > +#define NPCM_RNG_M1ROSEL     BIT(1)
> > +
> > +#define NPCM_RNG_TIMEOUT_POLL        20
>
> Might be better to define this in real-world units (such as
> milliseconds) since the timeout is effectively the longest time the
> hardware can take to generate 4 bytes.
>
> > +
> > +#define to_npcm_rng(p)       container_of(p, struct npcm_rng, rng)
> > +
> > +struct npcm_rng {
> > +     void __iomem *base;
> > +     struct hwrng rng;
> > +};
> > +
> > +static int npcm_rng_init(struct hwrng *rng)
> > +{
> > +     struct npcm_rng *priv = to_npcm_rng(rng);
> > +     u32 val;
> > +
> > +     val = readl(priv->base + NPCM_RNGCS_REG);
> > +     val |= NPCM_RNG_ENABLE;
> > +     writel(val, priv->base + NPCM_RNGCS_REG);
> > +
> > +     return 0;
> > +}
> > +
> > +static void npcm_rng_cleanup(struct hwrng *rng)
> > +{
> > +     struct npcm_rng *priv = to_npcm_rng(rng);
> > +     u32 val;
> > +
> > +     val = readl(priv->base + NPCM_RNGCS_REG);
> > +     val &= ~NPCM_RNG_ENABLE;
> > +     writel(val, priv->base + NPCM_RNGCS_REG);
> > +}
> > +
> > +static bool npcm_rng_wait_ready(struct hwrng *rng, bool wait)
> > +{
> > +     struct npcm_rng *priv = to_npcm_rng(rng);
> > +     int timeout_cnt = 0;
> > +     int ready;
> > +
> > +     ready = readl(priv->base + NPCM_RNGCS_REG) & NPCM_RNG_DATA_VALID;
> > +     while ((ready == 0) && (timeout_cnt < NPCM_RNG_TIMEOUT_POLL)) {
> > +             usleep_range(500, 1000);
> > +             ready = readl(priv->base + NPCM_RNGCS_REG) &
> > +                     NPCM_RNG_DATA_VALID;
> > +             timeout_cnt++;
> > +     }
> > +
> > +     return !!ready;
> > +}
>
> This looks like an open-coded version of readl_poll_timeout()... better
> to use the library function.
>
> Also the sleep looks a bit long to me. What is the generation rate of
> the peripheral? Most RNG drivers have short intervals between data
> generation so they use delays rather than sleeps (a.k.a.
> readl_poll_timeout_atomic() ).
>
> the HWRNG generate byte of random data in a few milliseconds so it is
better to use the sleep command.

>
> > +
> > +static int npcm_rng_read(struct hwrng *rng, void *buf, size_t max, bool
> wait)
> > +{
> > +     struct npcm_rng *priv = to_npcm_rng(rng);
> > +     int retval = 0;
> > +
> > +     pm_runtime_get_sync((struct device *)priv->rng.priv);
> > +
> > +     while (max >= sizeof(u32)) {
> > +             if (!npcm_rng_wait_ready(rng, wait))
> > +                     break;
>
> The code as currently written does not honour the wait parameter (e.g.
> it sleeps even when wait is false).
>
>
> > +
> > +             *(u32 *)buf = readl(priv->base + NPCM_RNGD_REG);
> > +             retval += sizeof(u32);
> > +             buf += sizeof(u32);
> > +             max -= sizeof(u32);
> > +     }
> > +
> > +     pm_runtime_mark_last_busy((struct device *)priv->rng.priv);
> > +     pm_runtime_put_sync_autosuspend((struct device *)priv->rng.priv);
> > +
> > +     return retval || !wait ? retval : -EIO;
> > +}
> > +
> > +static int npcm_rng_probe(struct platform_device *pdev)
> > +{
> > +     struct npcm_rng *priv;
> > +     struct resource *res;
> > +     u32 quality;
> > +     int ret;
> > +
> > +     priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> > +     if (!priv)
> > +             return -ENOMEM;
> > +
> > +     res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +     priv->base = devm_ioremap_resource(&pdev->dev, res);
> > +     if (IS_ERR(priv->base))
> > +             return PTR_ERR(priv->base);
> > +
> > +     priv->rng.name = pdev->name;
> > +#ifndef CONFIG_PM
> > +     priv->rng.init = npcm_rng_init;
> > +     priv->rng.cleanup = npcm_rng_cleanup;
> > +#endif
> > +     priv->rng.read = npcm_rng_read;
> > +     priv->rng.priv = (unsigned long)&pdev->dev;
> > +     if (of_property_read_u32(pdev->dev.of_node, "quality", &quality))
> > +             priv->rng.quality = 1000;
> > +     else
> > +             priv->rng.quality = quality;
> > +
> > +     writel(NPCM_RNG_M1ROSEL, priv->base + NPCM_RNGMODE_REG);
> > +#ifndef CONFIG_PM
> > +     writel(NPCM_RNG_CLK_SET_25MHZ, priv->base + NPCM_RNGCS_REG);
> > +#else
> > +     writel(NPCM_RNG_CLK_SET_25MHZ | NPCM_RNG_ENABLE,
> > +            priv->base + NPCM_RNGCS_REG);
> > +#endif
>
> If this initialization was moved to npcm_rng_init() then there would be
> no need for the additional ifdefing. It would also get rid of the
> (potentially slow) readl calls on the PM wakeup path.
>

But when the Kernel have PM configuration than the priv->rng.init is not
set and
*add_early_randomness* function is called. for the *add_early_randomness*
success
the hwrng need to enabled in the probe.

I will remove the ifdef and add local variable instead (as Milton Miller
suggested)


> > +
> > +     ret = devm_hwrng_register(&pdev->dev, &priv->rng);
> > +     if (ret) {
> > +             dev_err(&pdev->dev, "Failed to register rng device: %d\n",
> > +                     ret);
> > +             return ret;
> > +     }
> > +
> > +     dev_set_drvdata(&pdev->dev, priv);
> > +     pm_runtime_set_autosuspend_delay(&pdev->dev, 100);
> > +     pm_runtime_use_autosuspend(&pdev->dev);
> > +     pm_runtime_enable(&pdev->dev);
> > +
> > +     dev_info(&pdev->dev, "Random Number Generator Probed\n");
>
> Does the user need to know this every time we boot? There are lots of
> debug tools we can bring to bear if they are worried the device
> isn't probing.
>
>
> Daniel.
>
>
> > +
> > +     return 0;
> > +}
> > +
> > +static int npcm_rng_remove(struct platform_device *pdev)
> > +{
> > +     struct npcm_rng *priv = platform_get_drvdata(pdev);
> > +
> > +     hwrng_unregister(&priv->rng);
> > +     pm_runtime_disable(&pdev->dev);
> > +     pm_runtime_set_suspended(&pdev->dev);
> > +
> > +     return 0;
> > +}
> > +
> > +#ifdef CONFIG_PM
> > +static int npcm_rng_runtime_suspend(struct device *dev)
> > +{
> > +     struct npcm_rng *priv = dev_get_drvdata(dev);
> > +
> > +     npcm_rng_cleanup(&priv->rng);
> > +
> > +     return 0;
> > +}
> > +
> > +static int npcm_rng_runtime_resume(struct device *dev)
> > +{
> > +     struct npcm_rng *priv = dev_get_drvdata(dev);
> > +
> > +     return npcm_rng_init(&priv->rng);
> > +}
> > +#endif
> > +
> > +static const struct dev_pm_ops npcm_rng_pm_ops = {
> > +     SET_RUNTIME_PM_OPS(npcm_rng_runtime_suspend,
> > +                        npcm_rng_runtime_resume, NULL)
> > +     SET_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
> > +                             pm_runtime_force_resume)
> > +};
> > +
> > +static const struct of_device_id rng_dt_id[] = {
> > +     { .compatible = "nuvoton,npcm750-rng",  },
> > +     {},
> > +};
> > +MODULE_DEVICE_TABLE(of, rng_dt_id);
> > +
> > +static struct platform_driver npcm_rng_driver = {
> > +     .driver = {
> > +             .name           = "npcm-rng",
> > +             .pm             = &npcm_rng_pm_ops,
> > +             .owner          = THIS_MODULE,
> > +             .of_match_table = of_match_ptr(rng_dt_id),
> > +     },
> > +     .probe          = npcm_rng_probe,
> > +     .remove         = npcm_rng_remove,
> > +};
> > +
> > +module_platform_driver(npcm_rng_driver);
> > +
> > +MODULE_DESCRIPTION("Nuvoton NPCM Random Number Generator Driver");
> > +MODULE_AUTHOR("Tomer Maimon <tomer.maimon@nuvoton.com>");
> > +MODULE_LICENSE("GPL v2");
> > --
> > 2.18.0
> >
>

Thanks a lot,

Tomer

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