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Date: Mon, 5 Oct 2015 11:44:30 +0100
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Lee Jones <lee.jones@...aro.org>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
devicetree@...r.kernel.org, herbert@...dor.apana.org.au,
linux-crypto@...r.kernel.org, peter@...sgaard.com,
festevam@...il.com, kieranbingham@...il.com
Cc: kernel@...inux.com, Pankaj Dev <pankaj.dev@...com>
Subject: Re: [PATCH v2 5/7] hwrng: st: Add support for ST's HW Random Number
Generator
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: <pankaj.dev@...com>
> + * Lee Jones <lee.jones@...aro.org>
> + *
> + * 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.
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