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Subject[RFC PATCH 7/8] mtd: rawnand: ams-delta: Check sanity of data GPIO resource
Date
The plan is to replace data port readw()/writew() operations with GPIO
callbacks provided by gpio-omap driver. For acceptable performance the
GPIO chip must support get/set_multiple() GPIO callbacks.

In order to avoid data corruption, we require the array of data GPIO
descriptors obtained with gpiod_get_array() to meet some strict
requirements:
- all pins must belong to the same single GPIO chip,
- array index of each pin descriptor must match its hardware number,
- pin polarity must not be inverted,
- pin hardware configuration must not be open drain nor open source.

Let's implement the above described sanity checks before replacing the
readw()/writew() operations witn GPIO callbacks. If a check fails,
return -EINVAL to indicate the board provided GPIO setup is invalid.

Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
---
drivers/mtd/nand/raw/ams-delta.c | 87 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 86 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/raw/ams-delta.c b/drivers/mtd/nand/raw/ams-delta.c
index ad62c0245458..bd501f385e78 100644
--- a/drivers/mtd/nand/raw/ams-delta.c
+++ b/drivers/mtd/nand/raw/ams-delta.c
@@ -21,6 +21,7 @@
#include <linux/module.h>
#include <linux/delay.h>
#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/rawnand.h>
#include <linux/mtd/partitions.h>
@@ -190,7 +191,9 @@ static int ams_delta_init(struct platform_device *pdev)
struct resource *res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
void __iomem *io_base;
struct gpio_descs *data_gpiods;
- int err = 0;
+ struct gpio_chip *data_gpioc;
+ unsigned long mask, bits;
+ int i, err = 0;

if (!res)
return -ENXIO;
@@ -298,6 +301,88 @@ static int ams_delta_init(struct platform_device *pdev)
goto out_mtd;
}

+ /* Use GPIO chip of first data GPIO pin descriptor */
+ data_gpioc = gpiod_to_chip(data_gpiods->desc[0]);
+
+ /*
+ * For acceptable performance require the data GPIO
+ * chip to support get/set_multiple() callbacks.
+ */
+ if (!data_gpioc->get_multiple || !data_gpioc->set_multiple) {
+ err = -EINVAL;
+ dev_err(&pdev->dev,
+ "data GPIO chip does not support get/set_multiple()\n");
+ goto out_mtd;
+ }
+
+ /* Verify if get_multiple() returns all pins low as initialized above */
+ mask = (1 << data_gpiods->ndescs) - 1;
+ err = data_gpioc->get_multiple(data_gpioc, &mask, &bits);
+ if (err) {
+ dev_err(&pdev->dev,
+ "data GPIO chip get_multiple() failed: %d\n", err);
+ goto out_mtd;
+ }
+ if (bits) {
+ err = -EINVAL;
+ dev_err(&pdev->dev,
+ "mismmatch of data GPIO initial value: %lu\n", bits);
+ goto out_mtd;
+ }
+
+ /* Verify each data GPIO pin */
+ for (i = 0; i < data_gpiods->ndescs; i++) {
+ /* Require all pins belong to the same GPIO chip */
+ if (gpiod_to_chip(data_gpiods->desc[i]) != data_gpioc) {
+ err = -EINVAL;
+ dev_err(&pdev->dev, "GPIO chip mismatch of data bit %d\n",
+ i);
+ goto out_mtd;
+ }
+
+ /* Require all pins active high (not inverted) */
+ if (gpiod_is_active_low(data_gpiods->desc[i])) {
+ err = -EINVAL;
+ dev_err(&pdev->dev,
+ "unsupported polarity of data GPIO bit %d\n",
+ i);
+ goto out_mtd;
+ }
+
+ /*
+ * Require pin gpiod array index to match hardware pin number.
+ * Verified by setting the pin high with gpiod_set_raw_value()
+ * then reading it back with gpiochip->get() for comparison.
+ */
+ gpiod_set_raw_value(data_gpiods->desc[i], 1);
+ err = data_gpioc->get(data_gpioc, i);
+ if (err < 0) {
+ dev_err(&pdev->dev,
+ "data bit %d GPIO chip get() failed: %d\n", i,
+ err);
+ goto out_mtd;
+ }
+ if (!err) {
+ err = -EINVAL;
+ dev_err(&pdev->dev, "mismatch of data GPIO bit %d value\n",
+ i);
+ goto out_mtd;
+ }
+
+ /*
+ * Check for unsupported pin hardware configuration. Use
+ * just verified gpiod array index as hardware pin number.
+ */
+ if (gpiochip_line_is_open_drain(data_gpioc, i) ||
+ gpiochip_line_is_open_source(data_gpioc, i)) {
+ err = -EINVAL;
+ dev_err(&pdev->dev,
+ "unsupported mode of data GPIO bit %d\n",
+ i);
+ goto out_mtd;
+ }
+ }
+
/* Scan to find existence of the device */
err = nand_scan(mtd, 1);
if (err)
--
2.16.4
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