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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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