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RE: [PATCH 3/3] target/nios2: Use gen_io_start around wrctl instruction


From: Wu, Wentong
Subject: RE: [PATCH 3/3] target/nios2: Use gen_io_start around wrctl instruction
Date: Sun, 5 Jul 2020 13:24:42 +0000

Correct the format

> -----Original Message-----
> From: Richard Henderson <richard.henderson@linaro.org> 
> Sent: Friday, July 3, 2020 2:54 AM
> To: Wu, Wentong <wentong.wu@intel.com>; qemu-devel@nongnu.org
> Cc: qemu-trivial@nongnu.org; marex@denx.de; crwulff@gmail.com; 
> peter.maydell@linaro.org
> Subject: Re: [PATCH 3/3] target/nios2: Use gen_io_start around wrctl 
> instruction
> 
> On 6/29/20 9:05 AM, Wentong Wu wrote:
> > wrctl instruction on nios2 target will cause checking cpu interrupt 
> > but tcg_handle_interrupt() will call cpu_abort() if the CPU gets an 
> > interrupt while it's not in 'can do IO'
> > state, so add gen_io_start around wrctl instruction. Also at the same 
> > time, end the onging TB with DISAS_UPDATE.
> > 
> > Signed-off-by: Wentong Wu <wentong.wu@intel.com>
> > ---
> >  target/nios2/translate.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/target/nios2/translate.c b/target/nios2/translate.c index 
> > 83c10eb2..51347ada 100644
> > --- a/target/nios2/translate.c
> > +++ b/target/nios2/translate.c
> > @@ -32,6 +32,7 @@
> >  #include "exec/cpu_ldst.h"
> >  #include "exec/translator.h"
> >  #include "qemu/qemu-print.h"
> > +#include "exec/gen-icount.h"
> >  
> >  /* is_jmp field values */
> >  #define DISAS_JUMP    DISAS_TARGET_0 /* only pc was modified dynamically */
> > @@ -518,7 +519,11 @@ static void wrctl(DisasContext *dc, uint32_t code, 
> > uint32_t flags)
> >      /* If interrupts were enabled using WRCTL, trigger them. */  #if 
> > !defined(CONFIG_USER_ONLY)
> >      if ((instr.imm5 + CR_BASE) == CR_STATUS) {
> > +        if (tb_cflags(dc->tb) & CF_USE_ICOUNT) {
> > +            gen_io_start();
> > +        }
> >          gen_helper_check_interrupts(dc->cpu_env);
> > +        dc->is_jmp = DISAS_UPDATE;
> >      }
> >  #endif
> 
> This isn't right.  Not so much the gen_io_start portion, but the entire 
> existence of helper_check_interrupt.
> 
> The correct way to acknowledge interrupts after changing an interrupt mask 
> bit is to exit the TB back to the cpu main loop.
> Which you are doing here with DISAS_UPDATE, so that part is fine.  (Although 
> you could merge that into the switch statement above.)
> 
> Looking at nios_pic_cpu_handler, there are two other bugs:
> 
> 1) Get rid of env->irq_pending and use cpu_interrupt/cpu_reset_interrupt 
> instead.

IMHO, we need env->irq_pending, because if ((env->regs[CR_STATUS] & 
CR_STATUS_PIE) == False), it can indicate there is interrupt pending, we can 
exit to main loop to handle the interrupt at once if guest code enable irq 
later.

> 2) Do not check env->regs[CR_STATUS] & CR_STATUS_PIE.  That variable does not 
> belong to the pic and should not be checked there.  The check belongs in 
> nios2_cpu_exec_interrupt, and is in fact already there.

But that will cause some assert happen if device trigger irq with 
env->regs[CR_STATUS] & CR_STATUS_PIE = False

BR

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