Re: [Qemu-devel] [PATCH v3 02/35] ppc/xive: add support for the LSI interrupt sources

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Apr 23, 2018 at 09:31:24AM +0200, Cédric Le Goater wrote:
> On 04/23/2018 08:44 AM, David Gibson wrote:
> > On Thu, Apr 19, 2018 at 02:42:58PM +0200, Cédric Le Goater wrote:
> >> The 'sent' status of the LSI interrupt source is modeled with the 'P'
> >> bit of the ESB and the assertion status of the source is maintained in
> >> an array under the main sPAPRXive object. The type of the source is
> >> stored in the same array for practical reasons.
> >>
> >> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> >> ---
> >>  hw/intc/xive.c        | 54 +++++++++++++++++++++++++++++++++++++++++++++++----
> >>  include/hw/ppc/xive.h | 16 +++++++++++++++
> >>  2 files changed, 66 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/hw/intc/xive.c b/hw/intc/xive.c
> >> index c70578759d02..060976077dd7 100644
> >> --- a/hw/intc/xive.c
> >> +++ b/hw/intc/xive.c
> >> @@ -104,6 +104,21 @@ static void xive_source_notify(XiveSource *xsrc, int srcno)
> >>  
> >>  }
> >>  
> >> +/*
> >> + * LSI interrupt sources use the P bit and a custom assertion flag
> >> + */
> >> +static bool xive_source_lsi_trigger(XiveSource *xsrc, uint32_t srcno)
> >> +{
> >> +    uint8_t old_pq = xive_source_pq_get(xsrc, srcno);
> >> +
> >> +    if  (old_pq == XIVE_ESB_RESET &&
> >> +         xsrc->status[srcno] & XIVE_STATUS_ASSERTED) {
> >> +        xive_source_pq_set(xsrc, srcno, XIVE_ESB_PENDING);
> >> +        return true;
> >> +    }
> >> +    return false;
> >> +}
> >> +
> >>  /* In a two pages ESB MMIO setting, even page is the trigger page, odd
> >>   * page is for management */
> >>  static inline bool xive_source_is_trigger_page(hwaddr addr)
> >> @@ -133,6 +148,13 @@ static uint64_t xive_source_esb_read(void *opaque, hwaddr addr, unsigned size)
> >>           */
> >>          ret = xive_source_pq_eoi(xsrc, srcno);
> >>  
> >> +        /* If the LSI source is still asserted, forward a new source
> >> +         * event notification */
> >> +        if (xive_source_irq_is_lsi(xsrc, srcno)) {
> >> +            if (xive_source_lsi_trigger(xsrc, srcno)) {
> >> +                xive_source_notify(xsrc, srcno);
> >> +            }
> >> +        }
> >>          break;
> >>  
> >>      case XIVE_ESB_GET:
> >> @@ -183,6 +205,14 @@ static void xive_source_esb_write(void *opaque, hwaddr addr,
> >>           * notification
> >>           */
> >>          notify = xive_source_pq_eoi(xsrc, srcno);
> >> +
> >> +        /* LSI sources do not set the Q bit but they can still be
> >> +         * asserted, in which case we should forward a new source
> >> +         * event notification
> >> +         */
> >> +        if (xive_source_irq_is_lsi(xsrc, srcno)) {
> >> +            notify = xive_source_lsi_trigger(xsrc, srcno);
> >> +        }
> 
> FYI, I have moved that common test under xive_source_pq_eoi()

Ok.

> >>          break;
> >>  
> >>      default:
> >> @@ -216,8 +246,17 @@ static void xive_source_set_irq(void *opaque, int srcno, int val)
> >>      XiveSource *xsrc = XIVE_SOURCE(opaque);
> >>      bool notify = false;
> >>  
> >> -    if (val) {
> >> -        notify = xive_source_pq_trigger(xsrc, srcno);
> >> +    if (xive_source_irq_is_lsi(xsrc, srcno)) {
> >> +        if (val) {
> >> +            xsrc->status[srcno] |= XIVE_STATUS_ASSERTED;
> >> +        } else {
> >> +            xsrc->status[srcno] &= ~XIVE_STATUS_ASSERTED;
> >> +        }
> >> +        notify = xive_source_lsi_trigger(xsrc, srcno);
> >> +    } else {
> >> +        if (val) {
> >> +            notify = xive_source_pq_trigger(xsrc, srcno);
> >> +        }
> >>      }
> >>  
> >>      /* Forward the source event notification for routing */
> >> @@ -234,13 +273,13 @@ void xive_source_pic_print_info(XiveSource *xsrc, Monitor *mon)
> >>                     xsrc->offset, xsrc->offset + xsrc->nr_irqs - 1);
> >>      for (i = 0; i < xsrc->nr_irqs; i++) {
> >>          uint8_t pq = xive_source_pq_get(xsrc, i);
> >> -        uint32_t lisn = i  + xsrc->offset;
> >>  
> >>          if (pq == XIVE_ESB_OFF) {
> >>              continue;
> >>          }
> >>  
> >> -        monitor_printf(mon, "  %4x %c%c\n", lisn,
> >> +        monitor_printf(mon, "  %4x %s %c%c\n", i + xsrc->offset,
> >> +                       xive_source_irq_is_lsi(xsrc, i) ? "LSI" : "MSI",
> >>                         pq & XIVE_ESB_VAL_P ? 'P' : '-',
> >>                         pq & XIVE_ESB_VAL_Q ? 'Q' : '-');
> >>      }
> >> @@ -249,6 +288,12 @@ void xive_source_pic_print_info(XiveSource *xsrc, Monitor *mon)
> >>  static void xive_source_reset(DeviceState *dev)
> >>  {
> >>      XiveSource *xsrc = XIVE_SOURCE(dev);
> >> +    int i;
> >> +
> >> +    /* Keep the IRQ type */
> >> +    for (i = 0; i < xsrc->nr_irqs; i++) {
> >> +        xsrc->status[i] &= ~XIVE_STATUS_ASSERTED;
> >> +    }
> >>  
> >>      /* SBEs are initialized to 0b01 which corresponds to "ints off" */
> >>      memset(xsrc->sbe, 0x55, xsrc->sbe_size);
> >> @@ -273,6 +318,7 @@ static void xive_source_realize(DeviceState *dev, Error **errp)
> >>  
> >>      xsrc->qirqs = qemu_allocate_irqs(xive_source_set_irq, xsrc,
> >>                                       xsrc->nr_irqs);
> >> +    xsrc->status = g_malloc0(xsrc->nr_irqs);
> >>  
> >>      /* Allocate the SBEs (State Bit Entry). 2 bits, so 4 entries per byte */
> >>      xsrc->sbe_size = DIV_ROUND_UP(xsrc->nr_irqs, 4);
> >> diff --git a/include/hw/ppc/xive.h b/include/hw/ppc/xive.h
> >> index d92a50519edf..0b76dd278d9b 100644
> >> --- a/include/hw/ppc/xive.h
> >> +++ b/include/hw/ppc/xive.h
> >> @@ -33,6 +33,9 @@ typedef struct XiveSource {
> >>      uint32_t     nr_irqs;
> >>      uint32_t     offset;
> >>      qemu_irq     *qirqs;
> >> +#define XIVE_STATUS_LSI         0x1
> >> +#define XIVE_STATUS_ASSERTED    0x2
> >> +    uint8_t      *status;
> > 
> > I don't love the idea of mixing configuration information (STATUS_LSI)
> > with runtime state information (ASSERTED) in the same field.  Any
> > reason not to have these as parallel bitmaps.
> 
> none. I can change that. 

Ok.

> > Come to that.. is there a compelling reason to allow any individual
> > irq to be marked LSI or MSI, rather than using separate XiveSource
> > objects for MSIs and LSIs?
> 
> yes. I would have preferred two distinct interrupt source objects but 
> this is to be compatible with XICS, which uses only one. If we want
> to be able to change interrupt mode, the IRQ number space should be
> organized in the exact same way. Or we should change XICS also.
> 
> Also, the change (a bitmap) is really small.

Hrm, but since XIVE supports thousands of irqs, it could be quite a
large bitmap.

It's not impossible - in fact, not really even that hard - to change
the existing irq layout on xics.  It does need a new machine type
variant, of course.

> >>      /* PQ bits */
> >>      uint8_t      *sbe;
> > 
> > .. and come to that is there a reason to keep the ASSERTED bit in a
> > separate array from sbe?  AFAICT the actual 2-bit-per-irq layout is
> > never exposed to the guests.
> 
> indeed. we always use the xive_source_pq_get/set() helpers to 
> manipulate the PQ bits. So we could add an extra bit for the ASSERT 
> without too much changes. Could also we put the type there or would 
> you still prefer a bitmap ?  

I'd prefer the type (config information) be separate from the P, Q,
ASSERTED bits (state information).

> > Or, even re-use the Q bit for asserted in LSIs (but report it as
> > always 0 in the register read/write path).
> 
> I would prefer to add extra status bits. It is easier to debug.
> 
> Thanks,
> 
> C.
> 
> >> @@ -127,4 +130,17 @@ uint8_t xive_source_pq_set(XiveSource *xsrc, uint32_t srcno, uint8_t pq);
> >>  
> >>  void xive_source_pic_print_info(XiveSource *xsrc, Monitor *mon);
> >>  
> >> +static inline bool xive_source_irq_is_lsi(XiveSource *xsrc, uint32_t srcno)
> >> +{
> >> +    assert(srcno < xsrc->nr_irqs);
> >> +    return xsrc->status[srcno] & XIVE_STATUS_LSI;
> >> +}
> >> +
> >> +static inline void xive_source_irq_set(XiveSource *xsrc, uint32_t srcno,
> >> +                                       bool lsi)
> >> +{
> >> +    assert(srcno < xsrc->nr_irqs);
> >> +    xsrc->status[srcno] |= lsi ? XIVE_STATUS_LSI : 0;
> >> +}
> >> +
> >>  #endif /* PPC_XIVE_H */
> > 
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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