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Linux/AM3352: Cannot read INTC registers

David Taylor
Prodigy 130 points
Part Number: AM3352

Tool/software: Linux

Hi there,  I have been trying to follow the instructions in this thread on changing the gpio interrupt priority: https://e2e.ti.com/support/arm/sitara_arm/f/791/t/523690

First of all i wanted to read the current value of the INTC_ILRm registers, I have tried both devmem2 and omapconf to read 0x48200100 but i always get the follwong error. 

root:~# ./omapconf read 0x48200100
[ 6065.393717] Unhandled fault: external abort on non-linefetch (0x1018) at 0xb6e7d100
[ 6065.401448] pgd = dbb14000
[ 6065.404169] [b6e7d100] *pgd=9dfc4831, *pte=48200303, *ppte=48200a33

Even reading the INTC_REVISION register returns the same. So i've read other threads and I know that this error is returned when mapping memory for an unpowered and unclocked module. I can't see how the INTC module can be disabled since linux is booting and functioning correctly.

So i have also tried reading the INTC registers form the kernel driver irq-omap-intc. The following code builds and prints during boot but it always returns zero. 

static int __init omap_init_irq_of(struct device_node *node)
{
int ret;
int i;

omap_irq_base = of_iomap(node, 0);
if (WARN_ON(!omap_irq_base))
return -ENOMEM;

domain = irq_domain_add_linear(node, omap_nr_irqs,
&irq_generic_chip_ops, NULL);

for (i = 0; i < omap_nr_irqs; i++)
{
pr_info("INTC_ILR reg:0x%x val: 0x%x\n", (omap_irq_base + (INTC_ILR0 + (0x4 * i))), intc_readl(INTC_ILR0 + 0x4 * i));//96
}

read_intc_irl_n();
omap_irq_soft_reset();

ret = omap_alloc_gc_of(domain, omap_irq_base);
if (ret < 0)
irq_domain_remove(domain);

return ret;
}

So is it normal that the INTC registers are not readable or is it somehow possible that INTC module isn't enabled? I can't see it being likely that the INTC module can be disabled and I can't find INTC power and clock enable registers in the PRCM. 

Thanks in advance for any help you can offer. 

  • 0
    TI__Guru**** 393215 points
    The software team have been notified. They will respond here.
  • 0
    TI__Guru**** 170625 points
    Hi David,

    I confirm INTC can not be accessed by default from user space. I tried also from u-boot stage, and there I am able to access successfully:

    md [.b, .w, .l] address [# of objects]
    => md 0x48200000 1
    48200000: 00000050 P...
    => md 0x48200100 1
    48200100: 00000000 ....
    => md 0x48200010 1
    48200010: 00000000 ....


    I will check about the differences in INTC config between u-boot stage and linux kernel, and come back to you.

    Regards,
    Pavel
  • 0 in reply to Pavel Botev
    TI__Genius 15510 points
    See section 6.1.2 Register Protection. I believe this is getting set so that you cannot access the registers in user space.

    Steve K.
  • 0 in reply to Steve Kipisz
    TI__Guru**** 170625 points

    David,

    As Steve explained, the protection feature is preventing you from access the INTC registers from user space. You can edit the INTC driver with commenting the protection enable function:

    linux-kernel/drivers/irqchip/irq-omap-intc.c

    static int __init omap_init_irq(u32 base, struct device_node *node)
    {
    ....
    //if (ret == 0)
    //omap_irq_enable_protection();

    return ret;
    }

    With this update applied, you should be able to access the INTC registers from user space with devmem2 tool.

    Regarding your attempt to access these registers from kernel level, I think this is not correct. Let me know if you still need to print the INTC registers from within the kernel.

    Regards,
    Pavel