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".

---
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
===================================================================
@@ -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
===================================================================
@@ -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);

This looks like 2.6.26-worthy bugfix to me? But as commonly happens, that isn't terribly clear.

Manage atmel_lcdfb FIFO underflow rework

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".

Reworked following Andrew Morton comments.

---

Andrew Morton :

This error may append in latency sensitive cases : slow clock, matrix slot cycle bad configuration, too high pixel clock...

Ok incremental patch follows. Tell me if you prefer that I send a reworked one.

I also added might_sleep() annotation functions.

Ok, I try to adapt this comment in the reworked patch.

Index: drivers/video/atmel_lcdfb.c
===================================================================
@@ -361,6 +361,8 @@ static int atmel_lcdfb_check_var(struct 
 */

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);

@@ -405,6 +407,8 @@ static int atmel_lcdfb_set_par(struct fb

	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,
@@ -840,7 +844,8 @@ static int __init atmel_lcdfb_probe(stru
		goto unmap_mmio;
	}

- /* Initialize bottom half workqueue */
+ /* 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);
@@ -885,6 +890,7 @@ static int __init atmel_lcdfb_probe(stru
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);
@@ -922,6 +928,7 @@ static int __exit atmel_lcdfb_remove(str
	if (!sinfo)
		return 0;

+	cancel_work_sync(&sinfo->task);
	exit_backlight(sinfo);
	if (sinfo->atmel_lcdfb_power_control)
		sinfo->atmel_lcdfb_power_control(0);