read the memory mapped address - pcie - kernel hangs

Greg KH greg at
Wed Jan 8 14:45:03 EST 2020

On Thu, Jan 09, 2020 at 12:30:20AM +0530, Muni Sekhar wrote:
> Hi All,
> I have module with Xilinx FPGA. It implements UART(s), SPI(s),
> parallel I/O and interfaces them to the Host CPU via PCI Express bus.
> I see that my system freezes without capturing the crash dump for certain tests.
> I debugged this issue and it was tracked down to the ‘readl()’ in
> interrupt handler code
> In ISR, first reads the Interrupt Status register using ‘readl()’ as
> given below.
>     status = readl(ctrl->reg + INT_STATUS);
> And then clears the pending interrupts using ‘writel()’ as given blow.
>         writel(status, ctrl->reg + INT_STATUS);
> I've noticed a kernel hang if INT_STATUS register read again after
> clearing the pending interrupts.

Why would you read that register again after writing to it?

And are you sure you are reading/writing the correct size of the irq
field?  I thought it was a "word" not "long"?  But that might depend on
your hardware, do you have a pointer to the kernel driver source you are
using for all of this?


greg k-h

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