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Memfault Beyond the Launch

Kernel hangs while accessing the IO mapped memory

Started by rohshall December 16, 2008
Hi,

I am writing a framebuffer driver and the kernel seems to hang while
accessing the IO re-mapped memory.

Here is what I did:
In my platform specific file, I added the platform_device

Code:

#define DK_LCDC_BASE		AT91_CHIPSELECT_7

static struct resource lcdc_resources[] = {
	// Resource 0 is framebuffer
	[0] = {
		.start	= DK_LCDC_BASE + SZ_2M,
		.end	= DK_LCDC_BASE + SZ_4M - 1,
		.flags	= IORESOURCE_MEM,
	},
	// Resource 1 is register space
	[1] = {
		.start	= DK_LCDC_BASE,
		.end	= DK_LCDC_BASE + SZ_2M - 1,
		.flags	= IORESOURCE_MEM,
	},
};

static struct platform_device at91_lcdc_device = {
	.name		= "s1d13513fb",
	.id		= -1, // only one
	.dev		= {
				.platform_data		= NULL,
			  },
	.resource	= lcdc_resources,
	.num_resources	= ARRAY_SIZE(lcdc_resources),
};


And in the framebuffer driver, I added the platform_driver

Code:

static int __devinit
s1d13xxxfb_probe(struct platform_device *pdev)
{
.........

	if (!request_mem_region(pdev->resource[0].start,
		pdev->resource[0].end - pdev->resource[0].start +1, "s1d13xxxfb mem"))
{
		dev_dbg(&pdev->dev, "request_mem_region failed\n");
		ret = -EBUSY;
		goto bail;
	}

	if (!request_mem_region(pdev->resource[1].start,
		pdev->resource[1].end - pdev->resource[1].start +1, "s1d13xxxfb regs"))
{
		dev_dbg(&pdev->dev, "request_mem_region failed\n");
		ret = -EBUSY;
		goto bail;
	}

	default_par = info->par;
	default_par->regs = ioremap_nocache(pdev->resource[1].start,
			pdev->resource[1].end - pdev->resource[1].start +1);
	if (!default_par->regs) {
		printk(KERN_ERR PFX "unable to map registers\n");
		ret = -ENOMEM;
		goto bail;
	}
	info->pseudo_palette = default_par->pseudo_palette;

	info->screen_base = ioremap_nocache(pdev->resource[0].start,
			pdev->resource[0].end - pdev->resource[0].start +1);

	if (!info->screen_base) {
		printk(KERN_ERR PFX "unable to map framebuffer\n");
		ret = -ENOMEM;
		goto bail;
	}


Now, all this succeeds as observed by the debug messages. However, when I
access the IO memory using ioread16 or iowrite16 functions or even the old
readw or writew functions, the kernel crashes.

Why is it happening even after the success of request_mem_region and
ioremap calls?

I have tried the following:
1. Disable most of the other peripherals so that they don't interfere with
this peripheral.
2. Comment out the initialization code that acceses this IO memory and try
to access it from user space using cat > /dev/fb0.
But when I access it from a user space, the kernel hangs confirming that
indeed the problem is in the access.

Please help me identifying where I am going wrong.
rohshall wrote:
> Hi, > > I am writing a framebuffer driver and the kernel seems to hang while > accessing the IO re-mapped memory. >
<snip>
> > Please help me identifying where I am going wrong.
Be real helpful if you would identify the processor and the kernel. Scott

Memfault Beyond the Launch