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gpio: Add a way to read 3-way strapping pins

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Using the internal vs. external pull resistors it is possible to get
27 different combinations from 3 strapping pins. Add an implementation
of this.

This involves updating the sandbox GPIO driver to model external and
(weaker) internal pull resistors. The get_value() method now takes account
of what is driving a pin:

   sandbox: GPIOD_EXT_DRIVEN - in which case GPIO_EXT_HIGH provides the
          value
   outside source - in which case GPIO_EXT_PULL_UP/DOWN indicates the
          external state and we work the final state using those flags and
          the internal GPIOD_PULL_UP/DOWN flags

Of course the outside source does not really exist in sandbox. We are just
modelling it for test purpose.

Signed-off-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Glass
2021-02-04 21:22:09 -07:00
committed by Tom Rini
parent be04f1ab42
commit 8a45b22057
5 changed files with 232 additions and 5 deletions
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5
arch/sandbox/include/asm/gpio.h
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@@ -26,8 +26,11 @@
/* Our own private GPIO flags, which musn't conflict with GPIOD_... */
#define GPIOD_EXT_HIGH BIT(31) /* external source is high (else low) */
#define GPIOD_EXT_DRIVEN BIT(30) /* external source is driven */
#define GPIOD_EXT_PULL_UP BIT(29) /* GPIO has external pull-up */
#define GPIOD_EXT_PULL_DOWN BIT(28) /* GPIO has external pull-down */
#define GPIOD_SANDBOX_MASK GENMASK(31, 30)
#define GPIOD_EXT_PULL (BIT(28) | BIT(29))
#define GPIOD_SANDBOX_MASK GENMASK(31, 28)
/**
* Return the simulated value of a GPIO (used only in sandbox test code)