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SubjectRe: [PATCH v2 2/2] hwrng: npcm: add NPCM RNG driver
On September 9, 2019 around 7:40AM in somet timezone, Tomer Maimon wrote:
>+#define NPCM_RNG_TIMEOUT_USEC 20000
>+#define NPCM_RNG_POLL_USEC 1000

...

>+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 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;
>+ int ready;
>+
>+ pm_runtime_get_sync((struct device *)priv->rng.priv);
>+
>+ while (max >= sizeof(u32)) {
>+ ready = readl(priv->base + NPCM_RNGCS_REG) &
>+ NPCM_RNG_DATA_VALID;
>+ if (!ready) {
>+ if (wait) {
>+ if (readl_poll_timeout(priv->base + NPCM_RNGCS_REG,
>+ ready,
>+ ready & NPCM_RNG_DATA_VALID,
>+ NPCM_RNG_POLL_USEC,
>+ NPCM_RNG_TIMEOUT_USEC))
>+ break;
>+ } else {
>+ break;

This break is too far from the condition and deeply nested to follow.

And looking further, readl_poll_timeout will read and check the condition before
calling usleep, so the the initial readl and check is redundant

Rearrange to make wait determine if you call readl_poll_timeout or
readl / compare / break.

>+ }
>+ }
>+
>+ *(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;
>+ bool pm_dis = false;
>+ 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
>+ pm_dis = true;
>+ priv->rng.init = npcm_rng_init;
>+ priv->rng.cleanup = npcm_rng_cleanup;
>+#endif

if you move this down you can use one if (ENABLED_CONFIG_PM) {}

>+ 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);
>+ if (pm_dis)
>+ 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);

wait ... if we know the whole value here, why read/modify/write the value
in the init and cleanup hook? Save the io read and write the known value
... define the value to be written for clarity between enable/disable if
needed



>+
>+ ret = devm_hwrng_register(&pdev->dev, &priv->rng);
>+ if (ret) {
>+ dev_err(&pdev->dev, "Failed to register rng device: %d\n",
>+ ret);

need to disable if CONFIG_PM ?

>+ return ret;
>+ }
>+
>+ dev_set_drvdata(&pdev->dev, priv);

This should probably be before the register.

>+ pm_runtime_set_autosuspend_delay(&pdev->dev, 100);

So every 100ms power off, and if userspace does a read we
will poll every 1ms for upto 20ms.

If userspace says try once a second with -ENODELAY so no wait,
it never gets data.


Oh, and yes, rngd sets non-blocking, polls the descriptors,
and falls back to slow expensive software if no hardware
says it has data ready.

>+ pm_runtime_use_autosuspend(&pdev->dev);
>+ pm_runtime_enable(&pdev->dev);
>+
>+ return 0;
>+}
>+
>+static int npcm_rng_remove(struct platform_device *pdev)
>+{
>+ struct npcm_rng *priv = platform_get_drvdata(pdev);
>+
>+ hwrng_unregister(&priv->rng);

you did devm register, but call unregister directly?

>+ 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,

module_platform_driver will set owner, remove it here.

>+ .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
>
>

milton

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