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.hender...@microchip.com>
Signed-off-by: Purna Chandra Mandal <purna.man...@microchip.com>
---
  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.hender...@microchip.com>
+ * 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.hender...@microchip.com>");
+MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");


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