fbdev: sh_mobile_hdmi: implement locking

The SH-Mobile HDMI driver runs in several contexts: ISR, delayed work-queue,
task context, when called from the sh_mobile_lcdc framebuffer driver. This
creates ample race possibilities. Even though most these races are purely
theoretical, it is better to close them. To trace fb_info validity we install a
notification callback in the HDMI driver, and the only way for it to get to
driver internal data is by using struct sh_mobile_lcdc_chan, therefore it had
to be extracted into a separate common header.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 87 insertions, 16 deletions

diff --git a/drivers/video/sh_mobile_hdmi.c b/drivers/video/sh_mobile_hdmi.c
index a8cf9a510f30..56e44fd0a3af 100644
--- a/drivers/video/sh_mobile_hdmi.c
+++ b/drivers/video/sh_mobile_hdmi.c
@@ -26,6 +26,8 @@
 #include <video/sh_mobile_hdmi.h>
 #include <video/sh_mobile_lcdc.h>
 
+#include "sh_mobile_lcdcfb.h"
+
 #define HDMI_SYSTEM_CTRL                        0x00 /* System control */
 #define HDMI_L_R_DATA_SWAP_CTRL_RPKT            0x01 /* L/R data swap control,
                                                         bits 19..16 of 20-bit N for Audio Clock Regeneration packet */
@@ -209,6 +211,7 @@ struct sh_hdmi {
         struct clk *hdmi_clk;
         struct device *dev;
         struct fb_info *info;
+        struct mutex mutex;             /* Protect the info pointer */
         struct delayed_work edid_work;
         struct fb_var_screeninfo var;
 };
@@ -720,17 +723,21 @@ static irqreturn_t sh_hdmi_hotplug(int irq, void *dev_id)
         return IRQ_HANDLED;
 }
 
+/* locking:     called with info->lock held, or before register_framebuffer() */
 static void hdmi_display_on(void *arg, struct fb_info *info)
 {
+        /*
+         * info is guaranteed to be valid, when we are called, because our
+         * FB_EVENT_FB_UNBIND notify is also called with info->lock held
+         */
         struct sh_hdmi *hdmi = arg;
         struct sh_mobile_hdmi_info *pdata = hdmi->dev->platform_data;
 
         pr_debug("%s(%p): state %x\n", __func__, pdata->lcd_dev, info->state);
-        /*
-         * FIXME: not a good place to store fb_info. And we cannot nullify it
-         * even on monitor disconnect. What should the lifecycle be?
-         */
+
+        /* No need to lock */
         hdmi->info = info;
+
         switch (hdmi->hp_state) {
         case HDMI_HOTPLUG_EDID_DONE:
                 /* PS mode d->e. All functions are active */
@@ -744,6 +751,7 @@ static void hdmi_display_on(void *arg, struct fb_info *info)
         }
 }
 
+/* locking: called with info->lock held */
 static void hdmi_display_off(void *arg)
 {
         struct sh_hdmi *hdmi = arg;
@@ -766,6 +774,8 @@ static void edid_work_fn(struct work_struct *work)
         if (!pdata->lcd_dev)
                 return;
 
+        mutex_lock(&hdmi->mutex);
+
         if (hdmi->hp_state == HDMI_HOTPLUG_EDID_DONE) {
                 pm_runtime_get_sync(hdmi->dev);
                 /* A device has been plugged in */
@@ -776,21 +786,25 @@ static void edid_work_fn(struct work_struct *work)
                 msleep(10);
 
                 if (!hdmi->info)
-                        return;
+                        goto out;
 
                 acquire_console_sem();
 
                 /* HDMI plug in */
                 hdmi->info->var = hdmi->var;
-                if (hdmi->info->state != FBINFO_STATE_RUNNING)
+                if (hdmi->info->state != FBINFO_STATE_RUNNING) {
                         fb_set_suspend(hdmi->info, 0);
-                else
-                        hdmi_display_on(hdmi, hdmi->info);
+                } else {
+                        if (lock_fb_info(hdmi->info)) {
+                                hdmi_display_on(hdmi, hdmi->info);
+                                unlock_fb_info(hdmi->info);
+                        }
+                }
 
                 release_console_sem();
         } else {
                 if (!hdmi->info)
-                        return;
+                        goto out;
 
                 acquire_console_sem();
 
@@ -801,13 +815,61 @@ static void edid_work_fn(struct work_struct *work)
                 pm_runtime_put(hdmi->dev);
         }
 
+out:
+        mutex_unlock(&hdmi->mutex);
+
         pr_debug("%s(%p): end\n", __func__, pdata->lcd_dev);
 }
 
+static int sh_hdmi_notify(struct notifier_block *nb,
+                          unsigned long action, void *data);
+
+static struct notifier_block sh_hdmi_notifier = {
+        .notifier_call = sh_hdmi_notify,
+};
+
+static int sh_hdmi_notify(struct notifier_block *nb,
+                          unsigned long action, void *data)
+{
+        struct fb_event *event = data;
+        struct fb_info *info = event->info;
+        struct sh_mobile_lcdc_chan *ch = info->par;
+        struct sh_mobile_lcdc_board_cfg *board_cfg = &ch->cfg.board_cfg;
+        struct sh_hdmi *hdmi = board_cfg->board_data;
+
+        if (nb != &sh_hdmi_notifier || !hdmi || hdmi->info != info)
+                return NOTIFY_DONE;
+
+        switch(action) {
+        case FB_EVENT_FB_REGISTERED:
+                /* Unneeded, activation taken care by hdmi_display_on() */
+                break;
+        case FB_EVENT_FB_UNREGISTERED:
+                /*
+                 * We are called from unregister_framebuffer() with the
+                 * info->lock held. This is bad for us, because we can race with
+                 * the scheduled work, which has to call fb_set_suspend(), which
+                 * takes info->lock internally, so, edid_work_fn() cannot take
+                 * and hold info->lock for the whole function duration. Using an
+                 * additional lock creates a classical AB-BA lock up. Therefore,
+                 * we have to release the info->lock temporarily, synchronise
+                 * with the work queue and re-acquire the info->lock.
+                 */
+                unlock_fb_info(hdmi->info);
+                mutex_lock(&hdmi->mutex);
+                hdmi->info = NULL;
+                mutex_unlock(&hdmi->mutex);
+                lock_fb_info(hdmi->info);
+                return NOTIFY_OK;
+        }
+        return NOTIFY_DONE;
+}
+
 static int __init sh_hdmi_probe(struct platform_device *pdev)
 {
         struct sh_mobile_hdmi_info *pdata = pdev->dev.platform_data;
         struct resource *res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+        struct sh_mobile_lcdc_board_cfg *board_cfg;
         int irq = platform_get_irq(pdev, 0), ret;
         struct sh_hdmi *hdmi;
         long rate;
@@ -821,6 +883,7 @@ static int __init sh_hdmi_probe(struct platform_device *pdev)
                 return -ENOMEM;
         }
 
+        mutex_init(&hdmi->mutex);
         hdmi->dev = &pdev->dev;
 
         hdmi->hdmi_clk = clk_get(&pdev->dev, "ick");
@@ -878,9 +941,11 @@ static int __init sh_hdmi_probe(struct platform_device *pdev)
 #endif
 
         /* Set up LCDC callbacks */
-        pdata->lcd_chan->board_cfg.board_data = hdmi;
-        pdata->lcd_chan->board_cfg.display_on = hdmi_display_on;
-        pdata->lcd_chan->board_cfg.display_off = hdmi_display_off;
+        board_cfg = &pdata->lcd_chan->board_cfg;
+        board_cfg->owner = THIS_MODULE;
+        board_cfg->board_data = hdmi;
+        board_cfg->display_on = hdmi_display_on;
+        board_cfg->display_off = hdmi_display_off;
 
         INIT_DELAYED_WORK(&hdmi->edid_work, edid_work_fn);
 
@@ -907,6 +972,7 @@ eclkenable:
 erate:
         clk_put(hdmi->hdmi_clk);
 egetclk:
+        mutex_destroy(&hdmi->mutex);
         kfree(hdmi);
 
         return ret;
@@ -917,19 +983,24 @@ static int __exit sh_hdmi_remove(struct platform_device *pdev)
         struct sh_mobile_hdmi_info *pdata = pdev->dev.platform_data;
         struct sh_hdmi *hdmi = platform_get_drvdata(pdev);
         struct resource *res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+        struct sh_mobile_lcdc_board_cfg *board_cfg = &pdata->lcd_chan->board_cfg;
         int irq = platform_get_irq(pdev, 0);
 
-        pdata->lcd_chan->board_cfg.display_on = NULL;
-        pdata->lcd_chan->board_cfg.display_off = NULL;
-        pdata->lcd_chan->board_cfg.board_data = NULL;
+        board_cfg->display_on = NULL;
+        board_cfg->display_off = NULL;
+        board_cfg->board_data = NULL;
+        board_cfg->owner = NULL;
 
+        /* No new work will be scheduled, wait for running ISR */
         free_irq(irq, hdmi);
-        pm_runtime_disable(&pdev->dev);
+        /* Wait for already scheduled work */
         cancel_delayed_work_sync(&hdmi->edid_work);
+        pm_runtime_disable(&pdev->dev);
         clk_disable(hdmi->hdmi_clk);
         clk_put(hdmi->hdmi_clk);
         iounmap(hdmi->base);
         release_mem_region(res->start, resource_size(res));
+        mutex_destroy(&hdmi->mutex);
         kfree(hdmi);
 
         return 0;