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Old 12-10-2008, 10:52 AM   #1
rohshall
LQ Newbie
 
Registered: Oct 2008
Posts: 9

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Kernel crashes while accessing the IO mapped memory


Hi,

I am writing a framebuffer driver and the kernel seems to crash 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 crashes confirming that indeed the problem is in the access.

Please help me identifying where I am going wrong.
 
  


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crash, framebuffer, kernel


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