linux-kernel - riscv pending interrupts freezes the kernel, fixing by csr

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Message-ID: <0831fc40-267d-f974-8785-d304265837d5@vlsi.fi>
Date:   Tue, 11 Jul 2023 16:18:01 +0300
From:   Mikko Saari <Mikko.Saari@...i.fi>
To:     linux-kernel@...r.kernel.org
Subject: riscv pending interrupts freezes the kernel, fixing by csr_clear-call

Hello Linux! In earlier Linux Risc-V-patches (ultraembedded 4.20-kernel) 
there was interrupt handling implemented by following way in 
"linux/arch/riscv/kernel/irq.c".
-----------------------------------------------------------------------------kernel 
4.20
  case INTERRUPT_CAUSE_EXTERNAL:
#ifdef CONFIG_XILINX_INTC
                 {
                      unsigned int irq;
                         irq = xintc_get_irq();
                 next_irq:
                         BUG_ON(!irq);
                         generic_handle_irq(irq);

                         irq = xintc_get_irq();
                         if (irq != -1U) {
                 pr_debug("next irq: %d\n", irq);
                 goto next_irq;
             }
         }
                 csr_clear(sip, 1 << INTERRUPT_CAUSE_EXTERNAL);
#else
              handle_arch_irq(regs);
#endif
               break;
     default:
                 panic("unexpected interrupt cause");
-------------------------------------------------------------------------------

   However, in current Linux version (6.5) there is no corresponding   
csr_clear(sip, 1 << INTERRUPT_CAUSE_EXTERNAL)-call anywhere, at least I 
haven't been able to find it.
Instead I did a "quick and dirty" -fix to the file 
"linux/drivers/irqchip/irq-xilinx-intc.c" and put the corresponding 
call     csr_clear(CSR_SIP, IE_EIE);
to function
------------------------------------------------------------------------kernel 
6.5
  static void xil_intc_irq_handler(struct irq_desc *desc)
{
     struct irq_chip *chip = irq_desc_get_chip(desc);
     struct xintc_irq_chip *irqc;
     u32 pending;


     irqc = irq_data_get_irq_handler_data(&desc->irq_data);
     chained_irq_enter(chip, desc);
     do {
         pending = xintc_get_irq_local(irqc);
         if (pending == 0)
             break;
         generic_handle_irq(pending);
     } while (true);
     chained_irq_exit(chip, desc);
     csr_clear(CSR_SIP, IE_EIE);
}
---------------------------------------------------------------------------
Now the interrupts are not pending and the system is not halted as it 
was before for example while using spidevtest before the modifications. 
The call csr_clear() clears pending interrupts that would otherwise halt 
the Linux kernel.
I wonder if this should be fixed somehow more elegantly? I am grateful 
for any answers. I am just a beginner in the adventure of the driver 
development, and any sensible answer is real help :)
Best Regards, Mikko Saari