[RFC PATCH 2/3] ata: ahci-platform: Add ports-implemented dt bindings.

[Srinivas Kandagatla]

On some SOCs PORTS_IMPL register value is never programmed by the BIOS
and left at zero value. Which means that no sata ports are avaiable for
software. AHCI driver used to cope up with this by fabricating the
port_map if the PORTS_IMPL register is read zero, but recent patch
broke this workaround as zero value was valid for nvme disks.

This patch adds ports-implemented dt bindings as workaround for this issue
in a way that DT can dictate the port_map incase where the SOCs does not
program it already.

Fixes: 566d1827df2e ("libata: disable forced PORTS_IMPL for >= AHCI 1.3)
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla at linaro.org>
---
 Documentation/devicetree/bindings/ata/ahci-platform.txt | 11 +++++++++++
 drivers/ata/ahci_platform.c                             |  4 ++++
 2 files changed, 15 insertions(+)

diff --git a/Documentation/devicetree/bindings/ata/ahci-platform.txt b/Documentation/devicetree/bindings/ata/ahci-platform.txt
index 30df832..8165db3 100644
--- a/Documentation/devicetree/bindings/ata/ahci-platform.txt
+++ b/Documentation/devicetree/bindings/ata/ahci-platform.txt
@@ -32,6 +32,10 @@ Optional properties:
 - target-supply     : regulator for SATA target power
 - phys              : reference to the SATA PHY node
 - phy-names         : must be "sata-phy"
+- ports-implemented : Mask that indicates which ports that the HBA supports
+		      are available for software to use. Useful if PORTS_IMPL
+		      is not programmed by the BIOS, which is true with
+		      some embedded SOC's.
 
 Required properties when using sub-nodes:
 - #address-cells    : number of cells to encode an address
@@ -59,6 +63,13 @@ Examples:
 		target-supply = <&reg_ahci_5v>;
 	};
 
+	sata0: sata at 29000000 { /* Qualcomm APQ8064 */
+		compatible = "generic-ahci";
+		reg = <0x29000000 0x180>;
+		interrupts = <GIC_SPI 209 IRQ_TYPE_NONE>;
+		ports-implemented = <0x1>;
+	};
+
 With sub-nodes:
 	sata at f7e90000 {
 		compatible = "marvell,berlin2q-achi", "generic-ahci";
diff --git a/drivers/ata/ahci_platform.c b/drivers/ata/ahci_platform.c
index 4044233..ec8db80 100644
--- a/drivers/ata/ahci_platform.c
+++ b/drivers/ata/ahci_platform.c
@@ -42,6 +42,7 @@ static int ahci_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct ahci_host_priv *hpriv;
 	int rc;
+	u32 ports_impl;
 
 	hpriv = ahci_platform_get_resources(pdev);
 	if (IS_ERR(hpriv))
@@ -51,6 +52,9 @@ static int ahci_probe(struct platform_device *pdev)
 	if (rc)
 		return rc;
 
+	of_property_read_u32(dev->of_node,
+			     "ports-implemented", &hpriv->force_port_map);
+
 	if (of_device_is_compatible(dev->of_node, "hisilicon,hisi-ahci"))
 		hpriv->flags |= AHCI_HFLAG_NO_FBS | AHCI_HFLAG_NO_NCQ;
 
-- 
2.5.0