Subject: [PATCH v2 5/7] hwrng: st: Add support for ST's HW Random Number Generator

From: [email-masked] (Daniel Thompson)
Date: Mon, 5 Oct 2015 11:44:30 +0100

Hi Lee

Late but...

On 17/09/15 14:45, Lee Jones wrote:
> diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
> index 055bb01..8bcfb45 100644
> --- a/drivers/char/hw_random/Makefile
> +++ b/drivers/char/hw_random/Makefile
> @@ -30,4 +30,5 @@ obj-$(CONFIG_HW_RANDOM_TPM) += tpm-rng.o
>   obj-$(CONFIG_HW_RANDOM_BCM2835) += bcm2835-rng.o
>   obj-$(CONFIG_HW_RANDOM_IPROC_RNG200) += iproc-rng200.o
>   obj-$(CONFIG_HW_RANDOM_MSM) += msm-rng.o
> +obj-$(CONFIG_HW_RANDOM_ST) += st-rng.o
>   obj-$(CONFIG_HW_RANDOM_XGENE) += xgene-rng.o
> diff --git a/drivers/char/hw_random/st-rng.c b/drivers/char/hw_random/st-rng.c
> new file mode 100644
> index 0000000..8c8a435
> --- /dev/null
> +++ b/drivers/char/hw_random/st-rng.c
> @@ -0,0 +1,144 @@
> +/*
> + * ST Random Number Generator Driver ST's Platforms
> + *
> + * Author: Pankaj Dev: <[email-masked]>
> + *         Lee Jones <[email-masked]>
> + *
> + * Copyright (C) 2015 STMicroelectronics (R&D) Limited
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/delay.h>
> +#include <linux/hw_random.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +
> +/* Registers */
> +#define ST_RNG_STATUS_REG		0x20
> +#define ST_RNG_DATA_REG			0x24
> +
> +/* Registers fields */
> +#define ST_RNG_STATUS_BAD_SEQUENCE	BIT(0)
> +#define ST_RNG_STATUS_BAD_ALTERNANCE	BIT(1)
> +#define ST_RNG_STATUS_FIFO_FULL		BIT(5)
> +
> +#define ST_RNG_FIFO_SIZE		8
> +#define ST_RNG_SAMPLE_SIZE		2 /* 2 Byte (16bit) samples */
> +
> +/* Samples are available every 0.667us, which we round to 1us */
> +#define ST_RNG_FILL_FIFO_TIMEOUT   (1 * (ST_RNG_FIFO_SIZE / ST_RNG_SAMPLE_SIZE))
> +
> +struct st_rng_data {
> +	void __iomem	*base;
> +	struct clk	*clk;
> +	struct hwrng	ops;
> +};
> +
> +static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
> +{
> +	struct st_rng_data *ddata = (struct st_rng_data *)rng->priv;
> +	u32 status;
> +	int i;
> +
> +	if (max < sizeof(u16))
> +		return -EINVAL;
> +
> +	/* Wait until FIFO is full - max 4uS*/
> +	for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {
> +		status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);
> +		if (status & ST_RNG_STATUS_FIFO_FULL)
> +			break;
> +		udelay(1);

How much bandwidth does using udelay() cost? I think it could be >10% 
compared to a tighter polling loop.

> +	}
> +
> +	if (i == ST_RNG_FILL_FIFO_TIMEOUT)
> +		return 0;

Isn't a timeout an error condition?

> +
> +	for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
> +		*(u16 *)(data + i) =
> +			readl_relaxed(ddata->base + ST_RNG_DATA_REG);
> +
> +	return i;	/* No of bytes read */
> +}
> +
> +static int st_rng_probe(struct platform_device *pdev)
> +{
> +	struct st_rng_data *ddata;
> +	struct resource *res;
> +	struct clk *clk;
> +	void __iomem *base;
> +	int ret;
> +
> +	ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
> +	if (!ddata)
> +		return -ENOMEM;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	base = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(base))
> +		return PTR_ERR(base);
> +
> +	clk = devm_clk_get(&pdev->dev, NULL);
> +	if (IS_ERR(clk))
> +		return PTR_ERR(clk);
> +
> +	ret = clk_prepare_enable(clk);
> +	if (ret)
> +		return ret;
> +
> +	ddata->ops.priv	= (unsigned long)ddata;
> +	ddata->ops.read	= st_rng_read;
> +	ddata->ops.name	= pdev->name;
> +	ddata->base	= base;
> +	ddata->clk	= clk;
> +
> +	dev_set_drvdata(&pdev->dev, ddata);
> +
> +	ret = hwrng_register(&ddata->ops);
> +	if (ret) {
> +		dev_err(&pdev->dev, "Failed to register HW RNG\n");

Why shout about this particular error but not any others? Perhaps just 
rely on the driver core to report the error here?

> +		return ret;
> +	}
> +
> +	dev_info(&pdev->dev, "Successfully registered HW RNG\n");
> +
> +	return 0;
> +}
> +
> +static int st_rng_remove(struct platform_device *pdev)
> +{
> +	struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
> +
> +	hwrng_unregister(&ddata->ops);
> +
> +	clk_disable_unprepare(ddata->clk);

This mismatches the error paths in the probe function (there is no 
cleanup of clock counts in probe function).

Daniel.