atmel_lcdfb: FIFO underflow management

Manage atmel_lcdfb FIFO underflow

Resetting the LCD and DMA allows to fix screen shifting after a FIFO
underflow.  It follows reset sequence from errata "LCD Screen Shifting
After a Reset".

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Andrew Victor <linux@maxim.org.za>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 57 insertions, 1 deletions

diff --git a/drivers/video/atmel_lcdfb.c b/drivers/video/atmel_lcdfb.c
index b004036d4087..d335bb96b03b 100644
--- a/drivers/video/atmel_lcdfb.c
+++ b/drivers/video/atmel_lcdfb.c
@@ -379,6 +379,35 @@ static int atmel_lcdfb_check_var(struct fb_var_screeninfo *var,
         return 0;
 }
 
+/*
+ * LCD reset sequence
+ */
+static void atmel_lcdfb_reset(struct atmel_lcdfb_info *sinfo)
+{
+        might_sleep();
+
+        /* LCD power off */
+        lcdc_writel(sinfo, ATMEL_LCDC_PWRCON, sinfo->guard_time << ATMEL_LCDC_GUARDT_OFFSET);
+
+        /* wait for the LCDC core to become idle */
+        while (lcdc_readl(sinfo, ATMEL_LCDC_PWRCON) & ATMEL_LCDC_BUSY)
+                msleep(10);
+
+        /* DMA disable */
+        lcdc_writel(sinfo, ATMEL_LCDC_DMACON, 0);
+
+        /* wait for DMA engine to become idle */
+        while (lcdc_readl(sinfo, ATMEL_LCDC_DMACON) & ATMEL_LCDC_DMABUSY)
+                msleep(10);
+
+        /* LCD power on */
+        lcdc_writel(sinfo, ATMEL_LCDC_PWRCON,
+                (sinfo->guard_time << ATMEL_LCDC_GUARDT_OFFSET) | ATMEL_LCDC_PWR);
+
+        /* DMA enable */
+        lcdc_writel(sinfo, ATMEL_LCDC_DMACON, sinfo->default_dmacon);
+}
+
 /**
  *      atmel_lcdfb_set_par - Alters the hardware state.
  *      @info: frame buffer structure that represents a single frame buffer
@@ -401,6 +430,8 @@ static int atmel_lcdfb_set_par(struct fb_info *info)
         unsigned long clk_value_khz;
         unsigned long bits_per_line;
 
+        might_sleep();
+
         dev_dbg(info->device, "%s:\n", __func__);
         dev_dbg(info->device, "  * resolution: %ux%u (%ux%u virtual)\n",
                  info->var.xres, info->var.yres,
@@ -511,6 +542,8 @@ static int atmel_lcdfb_set_par(struct fb_info *info)
 
         /* Disable all interrupts */
         lcdc_writel(sinfo, ATMEL_LCDC_IDR, ~0UL);
+        /* Enable FIFO & DMA errors */
+        lcdc_writel(sinfo, ATMEL_LCDC_IER, ATMEL_LCDC_UFLWI | ATMEL_LCDC_OWRI | ATMEL_LCDC_MERI);
 
         /* ...wait for DMA engine to become idle... */
         while (lcdc_readl(sinfo, ATMEL_LCDC_DMACON) & ATMEL_LCDC_DMABUSY)
@@ -645,10 +678,26 @@ static irqreturn_t atmel_lcdfb_interrupt(int irq, void *dev_id)
         u32 status;
 
         status = lcdc_readl(sinfo, ATMEL_LCDC_ISR);
-        lcdc_writel(sinfo, ATMEL_LCDC_IDR, status);
+        if (status & ATMEL_LCDC_UFLWI) {
+                dev_warn(info->device, "FIFO underflow %#x\n", status);
+                /* reset DMA and FIFO to avoid screen shifting */
+                schedule_work(&sinfo->task);
+        }
+        lcdc_writel(sinfo, ATMEL_LCDC_ICR, status);
         return IRQ_HANDLED;
 }
 
+/*
+ * LCD controller task (to reset the LCD)
+ */
+static void atmel_lcdfb_task(struct work_struct *work)
+{
+        struct atmel_lcdfb_info *sinfo =
+                container_of(work, struct atmel_lcdfb_info, task);
+
+        atmel_lcdfb_reset(sinfo);
+}
+
 static int __init atmel_lcdfb_init_fbinfo(struct atmel_lcdfb_info *sinfo)
 {
         struct fb_info *info = sinfo->info;
@@ -824,6 +873,10 @@ static int __init atmel_lcdfb_probe(struct platform_device *pdev)
                 goto unmap_mmio;
         }
 
+        /* Some operations on the LCDC might sleep and
+         * require a preemptible task context */
+        INIT_WORK(&sinfo->task, atmel_lcdfb_task);
+
         ret = atmel_lcdfb_init_fbinfo(sinfo);
         if (ret < 0) {
                 dev_err(dev, "init fbinfo failed: %d\n", ret);
@@ -866,6 +919,7 @@ static int __init atmel_lcdfb_probe(struct platform_device *pdev)
 free_cmap:
         fb_dealloc_cmap(&info->cmap);
 unregister_irqs:
+        cancel_work_sync(&sinfo->task);
         free_irq(sinfo->irq_base, info);
 unmap_mmio:
         exit_backlight(sinfo);
@@ -903,6 +957,7 @@ static int __exit atmel_lcdfb_remove(struct platform_device *pdev)
         if (!sinfo)
                 return 0;
 
+        cancel_work_sync(&sinfo->task);
         exit_backlight(sinfo);
         if (sinfo->atmel_lcdfb_power_control)
                 sinfo->atmel_lcdfb_power_control(0);
diff --git a/include/video/atmel_lcdc.h b/include/video/atmel_lcdc.h
index ed64862c4e18..1ccf462b433a 100644
--- a/include/video/atmel_lcdc.h
+++ b/include/video/atmel_lcdc.h
@@ -37,6 +37,7 @@ struct atmel_lcdfb_info {
         struct fb_info          *info;
         void __iomem            *mmio;
         unsigned long           irq_base;
+        struct work_struct      task;
 
         unsigned int            guard_time;
         struct platform_device  *pdev;