ahci: Workaround for ThunderX Errata#22536

Due to Errata in ThunderX, HOST_IRQ_STAT should be
cleared before leaving the interrupt handler.
The patch attempts to satisfy the need.

Changes from V2:
- removed newfile
- code is now under CONFIG_ARM64

Changes from V1:
- Rebased on top of libata/for-4.6
- Moved ThunderX intr handler to new file

tj: Minor adjustments to comments.

Signed-off-by: Tirumalesh Chalamarla <[e-mail]>
Signed-off-by: Tejun Heo <[e-mail]>

drivers/ata/ahci.c

···
 {}
 #endif
 
+#ifdef CONFIG_ARM64
+/*
+ * Due to ERRATA#22536, ThunderX needs to handle HOST_IRQ_STAT differently.
+ * Workaround is to make sure all pending IRQs are served before leaving
+ * handler.
+ */
+static irqreturn_t ahci_thunderx_irq_handler(int irq, void *dev_instance)
+{
+	struct ata_host *host = dev_instance;
+	struct ahci_host_priv *hpriv;
+	unsigned int rc = 0;
+	void __iomem *mmio;
+	u32 irq_stat, irq_masked;
+	unsigned int handled = 1;
+
+	VPRINTK("ENTER\n");
+	hpriv = host->private_data;
+	mmio = hpriv->mmio;
+	irq_stat = readl(mmio + HOST_IRQ_STAT);
+	if (!irq_stat)
+		return IRQ_NONE;
+
+	do {
+		irq_masked = irq_stat & hpriv->port_map;
+		spin_lock(&host->lock);
+		rc = ahci_handle_port_intr(host, irq_masked);
+		if (!rc)
+			handled = 0;
+		writel(irq_stat, mmio + HOST_IRQ_STAT);
+		irq_stat = readl(mmio + HOST_IRQ_STAT);
+		spin_unlock(&host->lock);
+	} while (irq_stat);
+	VPRINTK("EXIT\n");
+
+	return IRQ_RETVAL(handled);
+}
+#endif
+
 /*
  * ahci_init_msix() - optionally enable per-port MSI-X otherwise defer
  * to single msi.
···
 	/* must set flag prior to save config in order to take effect */
 	if (ahci_broken_devslp(pdev))
 		hpriv->flags |= AHCI_HFLAG_NO_DEVSLP;
+
+#ifdef CONFIG_ARM64
+	if (pdev->vendor == 0x177d && pdev->device == 0xa01c)
+		hpriv->irq_handler = ahci_thunderx_irq_handler;
+#endif
 
 	/* save initial config */
 	ahci_pci_save_initial_config(pdev, hpriv);