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Subject[PATCH] atmel_lcdfb: FIFO underflow management rework
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);




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