HSI: omap-ssi: add clk change support

This adds support for frequency changes of the SSI
functional clock, which may occur due to DVFS.

Acked-by: Pavel Machek <[e-mail]>
Signed-off-By: Sebastian Reichel <[e-mail]>

drivers/hsi/controllers/omap_ssi.h

···
  * @gdd_tasklet: bottom half for DMA transfers
  * @gdd_trn: Array of GDD transaction data for ongoing GDD transfers
  * @lock: lock to serialize access to GDD
+ * @fck_nb: DVFS notfifier block
+ * @fck_rate: clock rate
  * @loss_count: To follow if we need to restore context or not
  * @max_speed: Maximum TX speed (Kb/s) set by the clients.
  * @sysconfig: SSI controller saved context
···
 	struct tasklet_struct	gdd_tasklet;
 	struct gdd_trn		gdd_trn[SSI_MAX_GDD_LCH];
 	spinlock_t		lock;
+	struct notifier_block	fck_nb;
 	unsigned long		fck_rate;
 	u32			loss_count;
 	u32			max_speed;
···
 	struct dentry *dir;
 #endif
 };
+
+void omap_ssi_port_update_fclk(struct hsi_controller *ssi,
+			       struct omap_ssi_port *omap_port);
 
 extern struct platform_driver ssi_port_pdriver;
 

drivers/hsi/controllers/omap_ssi_core.c

···
 	return rate;
 }
 
+static int ssi_clk_event(struct notifier_block *nb, unsigned long event,
+								void *data)
+{
+	struct omap_ssi_controller *omap_ssi = container_of(nb,
+					struct omap_ssi_controller, fck_nb);
+	struct hsi_controller *ssi = to_hsi_controller(omap_ssi->dev);
+	struct clk_notifier_data *clk_data = data;
+	struct omap_ssi_port *omap_port;
+	int i;
+
+	switch (event) {
+	case PRE_RATE_CHANGE:
+		dev_dbg(&ssi->device, "pre rate change\n");
+
+		for (i = 0; i < ssi->num_ports; i++) {
+			omap_port = omap_ssi->port[i];
+
+			if (!omap_port)
+				continue;
+
+			/* Workaround for SWBREAK + CAwake down race in CMT */
+			tasklet_disable(&omap_port->wake_tasklet);
+
+			/* stop all ssi communication */
+			pinctrl_pm_select_idle_state(omap_port->pdev);
+			udelay(1); /* wait for racing frames */
+		}
+
+		break;
+	case ABORT_RATE_CHANGE:
+		dev_dbg(&ssi->device, "abort rate change\n");
+		/* Fall through */
+	case POST_RATE_CHANGE:
+		dev_dbg(&ssi->device, "post rate change (%lu -> %lu)\n",
+			clk_data->old_rate, clk_data->new_rate);
+		omap_ssi->fck_rate = DIV_ROUND_CLOSEST(clk_data->new_rate, 1000); /* KHz */
+
+		for (i = 0; i < ssi->num_ports; i++) {
+			omap_port = omap_ssi->port[i];
+
+			if (!omap_port)
+				continue;
+
+			omap_ssi_port_update_fclk(ssi, omap_port);
+
+			/* resume ssi communication */
+			pinctrl_pm_select_default_state(omap_port->pdev);
+			tasklet_enable(&omap_port->wake_tasklet);
+		}
+
+		break;
+	default:
+		break;
+	}
+
+	return NOTIFY_DONE;
+}
+
 static int ssi_get_iomem(struct platform_device *pd,
 		const char *name, void __iomem **pbase, dma_addr_t *phy)
 {
···
 		goto out_err;
 	}
 
+	omap_ssi->fck_nb.notifier_call = ssi_clk_event;
+	omap_ssi->fck_nb.priority = INT_MAX;
+	clk_notifier_register(omap_ssi->fck, &omap_ssi->fck_nb);
+
 	/* TODO: find register, which can be used to detect context loss */
 	omap_ssi->get_loss = NULL;
 
···
 	int id = ssi->id;
 	tasklet_kill(&omap_ssi->gdd_tasklet);
 	hsi_unregister_controller(ssi);
+	clk_notifier_unregister(omap_ssi->fck, &omap_ssi->fck_nb);
 	ida_simple_remove(&platform_omap_ssi_ida, id);
 }
 

drivers/hsi/controllers/omap_ssi_port.c

···
 #include <linux/platform_device.h>
 #include <linux/dma-mapping.h>
 #include <linux/pm_runtime.h>
+#include <linux/delay.h>
 
 #include <linux/gpio/consumer.h>
 #include <linux/debugfs.h>
···
 
 	pm_runtime_get_sync(omap_port->pdev);
 	spin_lock_bh(&omap_port->lock);
+
+	/* stop all ssi communication */
+	pinctrl_pm_select_idle_state(omap_port->pdev);
+	udelay(1); /* wait for racing frames */
+
 	/* Stop all DMA transfers */
 	for (i = 0; i < SSI_MAX_GDD_LCH; i++) {
 		msg = omap_ssi->gdd_trn[i].msg;
···
 		ssi_flush_queue(&omap_port->rxqueue[i], NULL);
 	}
 	ssi_flush_queue(&omap_port->brkqueue, NULL);
+
+	/* Resume SSI communication */
+	pinctrl_pm_select_default_state(omap_port->pdev);
+
 	spin_unlock_bh(&omap_port->lock);
 	pm_runtime_put_sync(omap_port->pdev);
 
···
 
 	return 0;
 }
+
+void omap_ssi_port_update_fclk(struct hsi_controller *ssi,
+			       struct omap_ssi_port *omap_port)
+{
+	/* update divisor */
+	u32 div = ssi_calculate_div(ssi);
+	omap_port->sst.divisor = div;
+	ssi_restore_divisor(omap_port);
+}
+EXPORT_SYMBOL_GPL(omap_ssi_port_update_fclk);
 
 static int omap_ssi_port_runtime_suspend(struct device *dev)
 {