Re: [PATCH 2/4] gpiolib: add bitmask for valid GPIO lines

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Hi,

On 11/08/2017 04:37 AM, Timur Tabi wrote:
Add support for specifying that some GPIOs within a range are unavailable.
Some systems have a sparse list of GPIOs, where a range of GPIOs is
specified (usually 0 to n-1), but some subset within that range is
absent or unavailable for whatever reason.

To support this, allow drivers to specify a bitmask of GPIOs that
are present or absent.  Gpiolib will then block access to those that
are absent.

Signed-off-by: Timur Tabi <timur@xxxxxxxxxxxxxx>
---
  drivers/gpio/gpiolib.c      | 43 +++++++++++++++++++++++++++++++++++--------
  include/linux/gpio/driver.h |  2 ++
  2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 60553af4c004..c32387936cdd 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1481,22 +1481,36 @@ static struct gpio_chip *find_chip_by_name(const char *name)
static int gpiochip_irqchip_init_valid_mask(struct gpio_chip *gpiochip)
  {
-	if (!gpiochip->irq_need_valid_mask)
-		return 0;
+	if (gpiochip->irq_need_valid_mask) {
+		gpiochip->irq_valid_mask =
+			kcalloc(BITS_TO_LONGS(gpiochip->ngpio),
+				sizeof(long), GFP_KERNEL);
+		if (!gpiochip->irq_valid_mask)
+			return -ENOMEM;
- gpiochip->irq_valid_mask = kcalloc(BITS_TO_LONGS(gpiochip->ngpio),
-					   sizeof(long), GFP_KERNEL);
-	if (!gpiochip->irq_valid_mask)
-		return -ENOMEM;
+		/* Assume by default all GPIOs are valid */
+		bitmap_fill(gpiochip->irq_valid_mask, gpiochip->ngpio);
+	}
- /* Assume by default all GPIOs are valid */
-	bitmap_fill(gpiochip->irq_valid_mask, gpiochip->ngpio);
+	if (gpiochip->line_need_valid_mask) {
+		gpiochip->line_valid_mask =
+			kcalloc(BITS_TO_LONGS(gpiochip->ngpio),
+				sizeof(long), GFP_KERNEL);
+		if (!gpiochip->line_valid_mask)
+			return -ENOMEM;
+
+		/* Assume by default all GPIOs are valid */
+		bitmap_fill(gpiochip->line_valid_mask, gpiochip->ngpio);
+	}
return 0;
  }
static void gpiochip_irqchip_free_valid_mask(struct gpio_chip *gpiochip)
  {
+	kfree(gpiochip->line_valid_mask);
+	gpiochip->line_valid_mask = NULL;
+
  	kfree(gpiochip->irq_valid_mask);
  	gpiochip->irq_valid_mask = NULL;
  }
@@ -1510,6 +1524,15 @@ static bool gpiochip_irqchip_irq_valid(const struct gpio_chip *gpiochip,
  	return test_bit(offset, gpiochip->irq_valid_mask);
  }
+static bool gpiochip_irqchip_line_valid(const struct gpio_chip *gpiochip,
+					unsigned int offset)
+{
+	/* No mask means all valid */
+	if (likely(!gpiochip->line_valid_mask))
+		return true;
+	return test_bit(offset, gpiochip->line_valid_mask);
+}
+
  /**
   * gpiochip_set_cascaded_irqchip() - connects a cascaded irqchip to a gpiochip
   * @gpiochip: the gpiochip to set the irqchip chain to
@@ -3320,6 +3343,10 @@ struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
  		return desc;
  	}
+ /* Make sure the GPIO is valid before we request it. */
+	if (!gpiochip_irqchip_line_valid(desc->gdev->chip, idx))
+		return ERR_PTR(-EACCES);

We're hitting an issue here ^ when a consumer calls the devm_gpiod_get() API. This API
internally sets idx in gpiod_get_index to always 0. For example, in the call sequence
below, the idx argument to gpiochip_irqchip_line_valid is always 0:

devm_gpiod_get(dev, con_id, flags)
   devm_gpiod_get_index(dev, con_id, 0, flags)
      gpiod_get_index(dev, con_id, 0, flags)
         if (!gpiochip_irqchip_line_valid(desc->gdev->chip, 0))
             return ERR_PTR(-EACCES);

Therefore, with these patches, if we create a sparse gpio map, and the
0th gpio is set to "not accessible", all gpio requests end up failing with EACCESS
because idx is always passed as 0.

In gpiochip_irqchip_line_valid, shouldn't we test the nth bit (that corresponds to
this gpio_desc) in chip->line_valid_mask instead of idx passed above, which is always
0?

Thanks,
Archit


+
  	status = gpiod_request(desc, con_id);
  	if (status < 0)
  		return ERR_PTR(status);
diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index 424e5139ff10..853828ccabc8 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -173,6 +173,8 @@ struct gpio_chip {
  	bool			irq_nested;
  	bool			irq_need_valid_mask;
  	unsigned long		*irq_valid_mask;
+	bool			line_need_valid_mask;
+	unsigned long		*line_valid_mask;
  	struct lock_class_key	*lock_key;
  #endif

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