Re: [PATCH 2/2] rng: pic32-rng: Add PIC32 RNG hardware driver
From: Daniel Thompson
Date: Wed Feb 03 2016 - 06:23:04 EST
On 01/02/16 22:41, Joshua Henderson wrote:
Add support for the hardware pseudo and true random number generator
peripheral found on PIC32.
Signed-off-by: Joshua Henderson <joshua.henderson@xxxxxxxxxxxxx>
Signed-off-by: Purna Chandra Mandal <purna.mandal@xxxxxxxxxxxxx>
---
drivers/char/hw_random/Kconfig | 13 +++
drivers/char/hw_random/Makefile | 1 +
drivers/char/hw_random/pic32-rng.c | 152 ++++++++++++++++++++++++++++++++++++
3 files changed, 166 insertions(+)
create mode 100644 drivers/char/hw_random/pic32-rng.c
diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
index dbf2271..3ab0c46 100644
--- a/drivers/char/hw_random/Kconfig
+++ b/drivers/char/hw_random/Kconfig
@@ -381,6 +381,19 @@ config HW_RANDOM_STM32
If unsure, say N.
+config HW_RANDOM_PIC32
+ tristate "Microchip PIC32 Random Number Generator support"
+ depends on HW_RANDOM && MACH_PIC32
+ default y
+ ---help---
+ This driver provides kernel-side support for the Random Number
+ Generator hardware found on a PIC32.
+
+ To compile this driver as a module, choose M here. the
+ module will be called pic32-rng.
+
+ If unsure, say Y.
+
endif # HW_RANDOM
config UML_RANDOM
diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
index 5ad3976..f5a6fa7 100644
--- a/drivers/char/hw_random/Makefile
+++ b/drivers/char/hw_random/Makefile
@@ -33,3 +33,4 @@ obj-$(CONFIG_HW_RANDOM_MSM) += msm-rng.o
obj-$(CONFIG_HW_RANDOM_ST) += st-rng.o
obj-$(CONFIG_HW_RANDOM_XGENE) += xgene-rng.o
obj-$(CONFIG_HW_RANDOM_STM32) += stm32-rng.o
+obj-$(CONFIG_HW_RANDOM_PIC32) += pic32-rng.o
diff --git a/drivers/char/hw_random/pic32-rng.c b/drivers/char/hw_random/pic32-rng.c
new file mode 100644
index 0000000..d2f32c4
--- /dev/null
+++ b/drivers/char/hw_random/pic32-rng.c
@@ -0,0 +1,152 @@
+/*
+ * PIC32 RNG driver
+ *
+ * Joshua Henderson <joshua.henderson@xxxxxxxxxxxxx>
+ * Copyright (C) 2016 Microchip Technology Inc. All rights reserved.
+ *
+ * This program is free software; you can distribute it and/or modify it
+ * under the terms of the GNU General Public License (Version 2) as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/delay.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/hw_random.h>
+#include <linux/platform_device.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/clk.h>
+#include <linux/clkdev.h>
+
+#define RNGCON 0x04
+#define TRNGEN BIT(8)
+#define PRNGEN BIT(9)
+#define PRNGCONT BIT(10)
+#define TRNGMOD BIT(11)
+#define SEEDLOAD BIT(12)
+#define RNGPOLY1 0x08
+#define RNGPOLY2 0x0C
+#define RNGNUMGEN1 0x10
+#define RNGNUMGEN2 0x14
+#define RNGSEED1 0x18
+#define RNGSEED2 0x1C
+#define RNGRCNT 0x20
+#define RCNT_MASK 0x7F
+
+struct pic32_rng {
+ void __iomem *base;
+ struct hwrng rng;
+ struct clk *clk;
+};
+
+static int pic32_rng_read(struct hwrng *rng, void *buf, size_t max,
+ bool wait)
+{
+ struct pic32_rng *prng = container_of(rng, struct pic32_rng, rng);
+ u64 *data = buf;
+
+ *data = ((u64)readl(prng->base + RNGNUMGEN2) << 32) +
+ readl(prng->base + RNGNUMGEN1);
+ return 4;
+}
I have a number of questions at this point (although #3 is by far the
most important).
1. If the random number of 42-bit shouldn't this be return 5; ?
2. If you really do mean return 4; then why mess about with all the
shifting. You can just read and discard the upper 32-bits.
3. Why are you using the PRNG at all? The PRNG is a simple LSFR and
I don't think it ever gets reseeded at any point (meaning we get
almost no useful entropy from it at all).
Far better to read directly from the TRNG.
+
+static int pic32_rng_probe(struct platform_device *pdev)
+{
+ struct pic32_rng *prng;
+ struct resource *res;
+ u32 v, t;
+ int ret;
+
+ prng = devm_kzalloc(&pdev->dev, sizeof(*prng), GFP_KERNEL);
+ if (!prng)
+ return -ENOMEM;
+
+ res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+ prng->base = devm_ioremap_resource(&pdev->dev, res);
+ if (IS_ERR(prng->base))
+ return PTR_ERR(prng->base);
+
+ prng->clk = devm_clk_get(&pdev->dev, NULL);
+ if (IS_ERR(prng->clk))
+ return PTR_ERR(prng->clk);
+
+ clk_prepare_enable(prng->clk);
+
+ /* enable TRNG in enhanced mode */
+ v = readl(prng->base + RNGCON);
+ v &= ~(TRNGEN | PRNGEN | 0xff);
+ v |= TRNGMOD;
+ writel(v | TRNGEN, prng->base + RNGCON);
+
+ /* wait for valid seed */
+ usleep_range(100, 200);
+ t = readl(prng->base + RNGRCNT) & RCNT_MASK;
+ if (t < 0x2A)
+ dev_warn(&pdev->dev, "seed not generated.\n");
+
+ /* load initial seed */
+ writel(v | SEEDLOAD, prng->base + RNGCON);
+
+ /* load initial polynomial: 42bit poly */
+ writel(0x00c00003, prng->base + RNGPOLY1);
+ writel(0x00000000, prng->base + RNGPOLY2);
+
+ /* start PRNG to generate 42bit random */
+ v |= 0x2A | PRNGCONT | PRNGEN;
+ writel(v, prng->base + RNGCON);
+
+ prng->rng.name = pdev->name;
+ prng->rng.read = pic32_rng_read;
+
+ ret = hwrng_register(&prng->rng);
+ if (ret)
+ goto err_register;
+
+ platform_set_drvdata(pdev, prng);
+
+ return 0;
+
+err_register:
+ return ret;
Looks like we leak clock references on this error path.
+
+static int pic32_rng_remove(struct platform_device *pdev)
+{
+ struct pic32_rng *rng = platform_get_drvdata(pdev);
+
+ hwrng_unregister(&rng->rng);
+ writel(0, rng->base + RNGCON);
+ clk_disable_unprepare(rng->clk);
+ return 0;
+}
+
+static const struct of_device_id pic32_rng_of_match[] = {
+ { .compatible = "microchip,pic32mzda-rng", },
+ { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, pic32_rng_of_match);
+
+static struct platform_driver pic32_rng_driver = {
+ .probe = pic32_rng_probe,
+ .remove = pic32_rng_remove,
+ .driver = {
+ .name = "pic32-rng",
+ .owner = THIS_MODULE,
+ .of_match_table = of_match_ptr(pic32_rng_of_match),
+ },
+};
+
+module_platform_driver(pic32_rng_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Joshua Henderson <joshua.henderson@xxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");