[PATCH] atmel_lcdfb: FIFO underflow management

[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@atmel.com>
---
 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);

Re: [PATCH] atmel_lcdfb: FIFO underflow management

[Andrew Morton]

On Fri, 16 May 2008 14:34:12 +0200
Nicolas Ferre <nicolas.ferre@atmel.com> wrote:

> 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".
> 

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

> +	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;
>  }

Shouldn't there be a cancel_work_sync() in atmel_lcdfb_exit()?


> +	/* Initialize bottom half workqueue */

Well.  "bottom half" is an ancient term for softirqs, not for the
new-fangled process-context callbacks.

[PATCH] atmel_lcdfb: FIFO underflow management rework

[Nicolas Ferre]

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.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
---

Andrew Morton :
> On Fri, 16 May 2008 14:34:12 +0200
> Nicolas Ferre <nicolas.ferre@atmel.com> wrote:
> 
>> 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".
>>
> 
> This looks like 2.6.26-worthy bugfix to me?  But as commonly happens,
> that isn't terribly clear.

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

>> +	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;
>>  }
> 
> Shouldn't there be a cancel_work_sync() in atmel_lcdfb_exit()?

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

I also added  might_sleep() annotation functions.

>> +	/* Initialize bottom half workqueue */
> 
> Well.  "bottom half" is an ancient term for softirqs, not for the
> new-fangled process-context callbacks.

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


Index: drivers/video/atmel_lcdfb.c
===================================================================
--- a/drivers/video/atmel_lcdfb.c
+++ b/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);