linux-kernel - Re: [PATCH v3 2/3] hwrng: add Rockchip SoC hwrng driver

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Date: Fri, 21 Jun 2024 11:57:58 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Daniel Golle <daniel@...rotopia.org>,
 Aurelien Jarno <aurelien@...el32.net>, Olivia Mackall <olivia@...enic.com>,
 Herbert Xu <herbert@...dor.apana.org.au>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Heiko Stuebner <heiko@...ech.de>,
 Philipp Zabel <p.zabel@...gutronix.de>,
 Uwe Kleine-König <ukleinek@...ian.org>,
 Sebastian Reichel <sebastian.reichel@...labora.com>,
 Anand Moon <linux.amoon@...il.com>, Dragan Simic <dsimic@...jaro.org>,
 Sascha Hauer <s.hauer@...gutronix.de>, Martin Kaiser <martin@...ser.cx>,
 Ard Biesheuvel <ardb@...nel.org>, linux-crypto@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] hwrng: add Rockchip SoC hwrng driver

On 21/06/2024 03:25, Daniel Golle wrote:
> From: Aurelien Jarno <aurelien@...el32.net>
> 

> +
> +static int rk_rng_init(struct hwrng *rng)
> +{
> +	struct rk_rng *rk_rng = container_of(rng, struct rk_rng, rng);
> +	int ret;
> +
> +	/* start clocks */
> +	ret = clk_bulk_prepare_enable(rk_rng->clk_num, rk_rng->clk_bulks);
> +	if (ret < 0) {
> +		dev_err((struct device *) rk_rng->rng.priv,
> +			"Failed to enable clks %d\n", ret);
> +		return ret;
> +	}
> +
> +	/* set the sample period */
> +	writel(RK_RNG_SAMPLE_CNT, rk_rng->base + TRNG_RNG_SAMPLE_CNT);
> +
> +	/* set osc ring speed and enable it */
> +	writel_relaxed(TRNG_RNG_CTL_LEN_256_BIT |
> +		       TRNG_RNG_CTL_OSC_RING_SPEED_0 |
> +		       TRNG_RNG_CTL_ENABLE,
> +		       rk_rng->base + TRNG_RNG_CTL);

I doubt relaxed write is here intentional. Enabling should be last
instruction, so this should be ordered write.

> +
> +	return 0;
> +}
> +
> +static void rk_rng_cleanup(struct hwrng *rng)
> +{
> +	struct rk_rng *rk_rng = container_of(rng, struct rk_rng, rng);
> +
> +	/* stop TRNG */
> +	writel_relaxed(0, rk_rng->base + TRNG_RNG_CTL);

This should not be relaxed. This might lead to very tricky to debug issues.

> +
> +	/* stop clocks */
> +	clk_bulk_disable_unprepare(rk_rng->clk_num, rk_rng->clk_bulks);
> +}
> +
> +static int rk_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> +{
> +	struct rk_rng *rk_rng = container_of(rng, struct rk_rng, rng);
> +	size_t to_read = min_t(size_t, max, RK_RNG_MAX_BYTE);
> +	u32 reg;
> +	int ret = 0;
> +
> +	ret = pm_runtime_get_sync((struct device *) rk_rng->rng.priv);

Why this cannot be just simpler pm_runtime_resume_and_get()?

> +	if (ret < 0)
> +		goto out;

This does not look like correct error path. Device was not busy here.

> +
> +	/* Start collecting random data */
> +	writel_relaxed(TRNG_RNG_CTL_START, rk_rng->base + TRNG_RNG_CTL);
> +
> +	ret = readl_poll_timeout(rk_rng->base + TRNG_RNG_CTL, reg,
> +				 !(reg & TRNG_RNG_CTL_START),
> +				 RK_RNG_POLL_PERIOD_US,
> +				 RK_RNG_POLL_TIMEOUT_US);
> +	if (ret < 0)
> +		goto out;
> +
> +	/* Read random data stored in the registers */
> +	memcpy_fromio(buf, rk_rng->base + TRNG_RNG_DOUT, to_read);
> +out:
> +	pm_runtime_mark_last_busy((struct device *) rk_rng->rng.priv);
> +	pm_runtime_put_sync_autosuspend((struct device *) rk_rng->rng.priv);
> +
> +	return to_read;
> +}
> +
> +static int rk_rng_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct rk_rng *rk_rng;
> +	int ret;
> +
> +	rk_rng = devm_kzalloc(dev, sizeof(*rk_rng), GFP_KERNEL);
> +	if (!rk_rng)
> +		return -ENOMEM;
> +
> +	rk_rng->base = devm_platform_ioremap_resource(pdev, 0);
> +	if (IS_ERR(rk_rng->base))
> +		return PTR_ERR(rk_rng->base);
> +
> +	rk_rng->clk_num = devm_clk_bulk_get_all(dev, &rk_rng->clk_bulks);
> +	if (rk_rng->clk_num < 0)
> +		return dev_err_probe(dev, rk_rng->clk_num,
> +				     "Failed to get clks property\n");
> +
> +	rk_rng->rst = devm_reset_control_array_get(&pdev->dev, false, false);
> +	if (IS_ERR(rk_rng->rst))
> +		return dev_err_probe(dev, PTR_ERR(rk_rng->rst),
> +				     "Failed to get reset property\n");
> +
> +	reset_control_assert(rk_rng->rst);
> +	udelay(2);
> +	reset_control_deassert(rk_rng->rst);
> +
> +	platform_set_drvdata(pdev, rk_rng);
> +
> +	rk_rng->rng.name = dev_driver_string(dev);
> +#ifndef CONFIG_PM
> +	rk_rng->rng.init = rk_rng_init;
> +	rk_rng->rng.cleanup = rk_rng_cleanup;
> +#endif
> +	rk_rng->rng.read = rk_rng_read;
> +	rk_rng->rng.priv = (unsigned long) dev;
> +	rk_rng->rng.quality = 900;
> +
> +	pm_runtime_set_autosuspend_delay(dev, RK_RNG_AUTOSUSPEND_DELAY);
> +	pm_runtime_use_autosuspend(dev);
> +	pm_runtime_enable(dev);
> +
> +	ret = devm_hwrng_register(dev, &rk_rng->rng);
> +	if (ret)
> +		return dev_err_probe(&pdev->dev, ret, "Failed to register Rockchip hwrng\n");
> +
> +	dev_info(&pdev->dev, "Registered Rockchip hwrng\n");

Drop, driver should be silent on success.


Best regards,
Krzysztof