[PATCH] atmel_lcdfb: FIFO underflow management

[Nicolas Ferre]

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@xxxxxxxxx>
---
drivers/video/atmel_lcdfb.c |   50 +++++++++++++++++++++++++++++++++-
include/video/atmel_lcdc.h  |    1 
2 files changed, 50 insertions(+), 1 deletion(-)

Index: include/video/atmel_lcdc.h
===================================================================
--- 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;
Index: drivers/video/atmel_lcdfb.c
===================================================================
--- a/drivers/video/atmel_lcdfb.c
+++ b/drivers/video/atmel_lcdfb.c
@@ -356,6 +356,33 @@ static int atmel_lcdfb_check_var(struct 
	return 0;
}

+/*
+ * LCD reset sequence
+ */
+static void atmel_lcdfb_reset(struct atmel_lcdfb_info *sinfo)
+{
+	/* 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
@@ -486,6 +513,8 @@ static int atmel_lcdfb_set_par(struct fb

	/* 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)
@@ -620,10 +649,26 @@ static irqreturn_t atmel_lcdfb_interrupt
	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;
@@ -795,6 +840,9 @@ static int __init atmel_lcdfb_probe(stru
		goto unmap_mmio;
	}

+	/* Initialize bottom half workqueue */
+	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);



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