Re: [PATCH 2/7] hw/ppc: Implement S0 SBE interrupt as cpu_pause then host reset

[Harsh Prateek Bora <harshpb@linux.ibm.com>]

On 2/17/25 12:49, Aditya Gupta wrote:
> SBE's implementation of S0 seems to be basically "stop all clocks" and
> then "host reset"
> 
> Nearest equivalent to the stop clocks seems to be 'pause_all_vcpus' in
> QEMU,
> 
> Then reset the host, which is 'SHUTDOWN_CAUSE_GUEST_RESET' in QEMU.
> 
> Implement the S0 interrupt as pause_vcpus + guest_reset
> 
> See 'stopClocksS0' in SBE source code for more information.
> 
> Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
> ---
>   hw/ppc/pnv_sbe.c | 50 +++++++++++++++++++++++++++++++++++++++---------
>   1 file changed, 41 insertions(+), 9 deletions(-)
> 
> diff --git a/hw/ppc/pnv_sbe.c b/hw/ppc/pnv_sbe.c
> index 62c94a04a2df..a6bf13650f2d 100644
> --- a/hw/ppc/pnv_sbe.c
> +++ b/hw/ppc/pnv_sbe.c
> @@ -21,6 +21,8 @@
>   #include "qapi/error.h"
>   #include "qemu/log.h"
>   #include "qemu/module.h"
> +#include "system/cpus.h"
> +#include "system/runstate.h"
>   #include "hw/irq.h"
>   #include "hw/qdev-properties.h"
>   #include "hw/ppc/pnv.h"
> @@ -80,6 +82,15 @@
>   #define SBE_CONTROL_REG_S0              PPC_BIT(14)
>   #define SBE_CONTROL_REG_S1              PPC_BIT(15)
>   
> +static void pnv_sbe_set_host_doorbell(PnvSBE *sbe, uint64_t val)
> +{
> +    val &= SBE_HOST_RESPONSE_MASK; /* Is this right? What does HW do? */
> +    sbe->host_doorbell = val;
> +
> +    trace_pnv_sbe_reg_set_host_doorbell(val);
> +    qemu_set_irq(sbe->psi_irq, !!val);
> +}
> +
>   struct sbe_msg {
>       uint64_t reg[4];
>   };
> @@ -104,6 +115,7 @@ static uint64_t pnv_sbe_power9_xscom_ctrl_read(void *opaque, hwaddr addr,
>   static void pnv_sbe_power9_xscom_ctrl_write(void *opaque, hwaddr addr,
>                                          uint64_t val, unsigned size)
>   {
> +    PnvSBE *sbe = opaque;
>       uint32_t offset = addr >> 3;
>   
>       trace_pnv_sbe_xscom_ctrl_write(addr, val);
> @@ -113,6 +125,35 @@ static void pnv_sbe_power9_xscom_ctrl_write(void *opaque, hwaddr addr,
>           switch (val) {
>           case SBE_CONTROL_REG_S0:
>               qemu_log_mask(LOG_UNIMP, "SBE: S0 Interrupt triggered\n");
> +
> +            pnv_sbe_set_host_doorbell(sbe, sbe->host_doorbell | SBE_HOST_RESPONSE_MASK);
> +
> +            /*
> +             * Looks like, SBE stops clocks for all cores in S0.
> +             * See 'stopClocksS0' in SBE source code.
> +             * Nearest equivalent in QEMU seems to be 'pause_all_vcpus'
> +             */
> +            pause_all_vcpus();
> +
> +            /*
> +             * TODO: Pass `mpipl` node in device tree to signify next
> +             * boot is an MPIPL boot
> +             */
> +
> +            /* Then do a guest reset */
> +            /*
> +             * Requirement:
> +             * This guest reset should not clear the memory (which is
> +             * the case when this is merged)

This comment may need a rephrase. Also, if we are keeping an assumption 
that SHUTDOWN_CAUSE_GUEST_RESET should not clear the memory, it may be 
better to put a comment about this wherever it is handled as well.

> +             */
> +            qemu_system_reset_request(SHUTDOWN_CAUSE_GUEST_RESET);
> +
> +            /*
> +             * XXX: Does SBE really do system reset or only stop
> +             * clocks ? OPAL seems to think that control will not come
> +             * to it after it has triggered S0 interrupt.
> +             */
> +
>               break;
>           case SBE_CONTROL_REG_S1:
>               qemu_log_mask(LOG_UNIMP, "SBE: S1 Interrupt triggered\n");
> @@ -138,15 +179,6 @@ static const MemoryRegionOps pnv_sbe_power9_xscom_ctrl_ops = {
>       .endianness = DEVICE_BIG_ENDIAN,
>   };
>   
> -static void pnv_sbe_set_host_doorbell(PnvSBE *sbe, uint64_t val)
> -{
> -    val &= SBE_HOST_RESPONSE_MASK; /* Is this right? What does HW do? */
> -    sbe->host_doorbell = val;
> -
> -    trace_pnv_sbe_reg_set_host_doorbell(val);
> -    qemu_set_irq(sbe->psi_irq, !!val);
> -}
> -

Code movement like above could be a separate patch, not necessary though.
Patch 1 can be squashed with this one.

Thanks
Harsh
>   /* SBE Target Type */
>   #define SBE_TARGET_TYPE_PROC            0x00
>   #define SBE_TARGET_TYPE_EX              0x01