pinctrl-baytrail: add function mux checking in gpio pin request

The requested gpio pin must has the func_pin_mux field set
to GPIO function by BIOS/FW in advanced. Else, the gpio pin
request would fail. This is to ensure that we do not expose
any gpio pins which shall be used for alternate functions,
for eg: wakeup pin, I/O interfaces for LPSS, etc.

Signed-off-by: Chew, Kean Ho <kean.ho.chew@intel.com>
Signed-off-by: Chew, Chiau Ee <chiau.ee.chew@intel.com>
Reviewed-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 39 insertions, 3 deletions

diff --git a/drivers/pinctrl/pinctrl-baytrail.c b/drivers/pinctrl/pinctrl-baytrail.c
index 665b96bc0c3a..bf2b3f655469 100644
--- a/drivers/pinctrl/pinctrl-baytrail.c
+++ b/drivers/pinctrl/pinctrl-baytrail.c
@@ -60,6 +60,10 @@
 #define BYT_NGPIO_NCORE         28
 #define BYT_NGPIO_SUS           44
 
+#define BYT_SCORE_ACPI_UID      "1"
+#define BYT_NCORE_ACPI_UID      "2"
+#define BYT_SUS_ACPI_UID        "3"
+
 /*
  * Baytrail gpio controller consist of three separate sub-controllers called
  * SCORE, NCORE and SUS. The sub-controllers are identified by their acpi UID.
@@ -102,17 +106,17 @@ static unsigned const sus_pins[BYT_NGPIO_SUS] = {
 
 static struct pinctrl_gpio_range byt_ranges[] = {
         {
-                .name = "1", /* match with acpi _UID in probe */
+                .name = BYT_SCORE_ACPI_UID, /* match with acpi _UID in probe */
                 .npins = BYT_NGPIO_SCORE,
                 .pins = score_pins,
         },
         {
-                .name = "2",
+                .name = BYT_NCORE_ACPI_UID,
                 .npins = BYT_NGPIO_NCORE,
                 .pins = ncore_pins,
         },
         {
-                .name = "3",
+                .name = BYT_SUS_ACPI_UID,
                 .npins = BYT_NGPIO_SUS,
                 .pins = sus_pins,
         },
@@ -145,9 +149,41 @@ static void __iomem *byt_gpio_reg(struct gpio_chip *chip, unsigned offset,
         return vg->reg_base + reg_offset + reg;
 }
 
+static bool is_special_pin(struct byt_gpio *vg, unsigned offset)
+{
+        /* SCORE pin 92-93 */
+        if (!strcmp(vg->range->name, BYT_SCORE_ACPI_UID) &&
+                offset >= 92 && offset <= 93)
+                return true;
+
+        /* SUS pin 11-21 */
+        if (!strcmp(vg->range->name, BYT_SUS_ACPI_UID) &&
+                offset >= 11 && offset <= 21)
+                return true;
+
+        return false;
+}
+
 static int byt_gpio_request(struct gpio_chip *chip, unsigned offset)
 {
         struct byt_gpio *vg = to_byt_gpio(chip);
+        void __iomem *reg = byt_gpio_reg(chip, offset, BYT_CONF0_REG);
+        u32 value;
+        bool special;
+
+        /*
+         * In most cases, func pin mux 000 means GPIO function.
+         * But, some pins may have func pin mux 001 represents
+         * GPIO function. Only allow user to export pin with
+         * func pin mux preset as GPIO function by BIOS/FW.
+         */
+        value = readl(reg) & BYT_PIN_MUX;
+        special = is_special_pin(vg, offset);
+        if ((special && value != 1) || (!special && value)) {
+                dev_err(&vg->pdev->dev,
+                        "pin %u cannot be used as GPIO.\n", offset);
+                return -EINVAL;
+        }
 
         pm_runtime_get(&vg->pdev->dev);