[PATCH] i.MX6 PCIe: Fix imx6_pcie_deassert_core_reset() polarity

[khalasa@piap.pl (Krzysztof Hałasa)]

A recent commit 5c5fb40de8f14391a1238db05cef88754faf9229 stated:
Follows: linus/v4.4-rc2
Precedes: linus/v4.5-rc1

    PCI: imx6: Add support for active-low reset GPIO

    We previously used of_get_named_gpio(), which ignores the OF flags cell, so
    the reset GPIO defaulted to "active high." This doesn't work on the Toradex
    Apalis SoM with Ixora base board, which has an active-low reset GPIO.

    Use devm_gpiod_get_optional() instead so we pay attention to the active
    high/low flag.  This also adds support for GPIOs described via ACPI.

The (now replaced) code doesn't support the above:
@@ -287,10 +287,10 @@ static int imx6_pcie_deassert_core_reset(struct pcie_port *pp)
     usleep_range(200, 500);
 
     /* Some boards don't have PCIe reset GPIO. */
-    if (gpio_is_valid(imx6_pcie->reset_gpio)) {
-        gpio_set_value_cansleep(imx6_pcie->reset_gpio, 0);
+    if (imx6_pcie->reset_gpio) {
+        gpiod_set_value_cansleep(imx6_pcie->reset_gpio, 0);
         msleep(100);
-        gpio_set_value_cansleep(imx6_pcie->reset_gpio, 1);
+        gpiod_set_value_cansleep(imx6_pcie->reset_gpio, 1);
     }
     return 0;

If the reset_gpio setup code had ignored the flags (haven't checked
that), then clearly the resets were active-low (most reset lines are,
because they can be then driven with open-drain/collector output).
The gpiod_set_value*(0) activates reset, gpiod_set_value(1) -
deactivates.

Now we're told the setup code is now level-aware, but the above sequence
thus _deactivates_ reset for 100 ms, then _activates_ it again. It has
no chance to work, unless a board has a broken DTS file. A quick grep
shows that about half the IMX6 boards specify an active-low PCIe reset,
4 ask for active-high, and another 4 don't bother.


I wonder if all boards (except maybe that Toradex set) use an active-low
PCIe reset and are now broken. Perhaps Toradex uses active-high and thus
works.

I'm not fixing individual DTS files because I don't really know, though
perhaps we should change them all to "active-low", since it would work
the same as before the 5c5fb40de8f14391a1238db05cef88754faf9229 change.

Confirmed to fix Gateworks Laguna GW54xx.
Without the patch, the following happens (as expected):

PCI host bridge /soc/pcie@0x01000000 ranges:
  No bus range found for /soc/pcie@0x01000000, using [bus 00-ff]
   IO 0x01f80000..0x01f8ffff -> 0x00000000
  MEM 0x01000000..0x01efffff -> 0x01000000
imx6q-pcie 1ffc000.pcie: phy link never came up

Signed-off-by: Krzysztof Hałasa <khalasa@piap.pl>

diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
index fe60096..f17fb02 100644
--- a/drivers/pci/host/pci-imx6.c
+++ b/drivers/pci/host/pci-imx6.c
@@ -288,9 +288,9 @@ static int imx6_pcie_deassert_core_reset(struct pcie_port *pp)
 
 	/* Some boards don't have PCIe reset GPIO. */
 	if (imx6_pcie->reset_gpio) {
-		gpiod_set_value_cansleep(imx6_pcie->reset_gpio, 0);
-		msleep(100);
 		gpiod_set_value_cansleep(imx6_pcie->reset_gpio, 1);
+		msleep(100);
+		gpiod_set_value_cansleep(imx6_pcie->reset_gpio, 0);
 	}
 	return 0;