Re: [PATCH 07/50] ppc/xive2: Reset Generation Flipped bit on END Cache Watch

[Mike Kowal]

On 5/11/2025 10:10 PM, Nicholas Piggin wrote:

From: Michael Kowal <ko...@linux.ibm.com>

When the END Event Queue wraps the END EQ Generation bit is flipped and the
Generation Flipped bit is set to one.  On a END cache Watch read operation,
the Generation Flipped bit needs to be reset.

While debugging an error modified END not valid error messages to include
the method since all were the same.

Reviewed-by: Michael Kowal <ko...@linux.ibm.com>

Thanks MAK

Signed-off-by: Michael Kowal <ko...@linux.ibm.com>
---
  hw/intc/pnv_xive2.c | 3 ++-
  hw/intc/xive2.c     | 4 ++--
  2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/hw/intc/pnv_xive2.c b/hw/intc/pnv_xive2.c
index 30b4ab2efe..72cdf0f20c 100644
--- a/hw/intc/pnv_xive2.c
+++ b/hw/intc/pnv_xive2.c
@@ -1325,10 +1325,11 @@ static uint64_t pnv_xive2_ic_vc_read(void *opaque, 
hwaddr offset,
      case VC_ENDC_WATCH3_DATA0:
          /*
           * Load DATA registers from cache with data requested by the
-         * SPEC register
+         * SPEC register.  Clear gen_flipped bit in word 1.
           */
          watch_engine = (offset - VC_ENDC_WATCH0_DATA0) >> 6;
          pnv_xive2_end_cache_load(xive, watch_engine);
+        xive->vc_regs[reg] &= ~(uint64_t)END2_W1_GEN_FLIPPED;
          val = xive->vc_regs[reg];
          break;

diff --git a/hw/intc/xive2.c b/hw/intc/xive2.c

index 4dd04a0398..453fe37f18 100644
--- a/hw/intc/xive2.c
+++ b/hw/intc/xive2.c
@@ -374,8 +374,8 @@ static void xive2_end_enqueue(Xive2End *end, uint32_t data)
          qgen ^= 1;
          end->w1 = xive_set_field32(END2_W1_GENERATION, end->w1, qgen);

- /* TODO(PowerNV): reset GF bit on a cache watch operation */

-        end->w1 = xive_set_field32(END2_W1_GEN_FLIPPED, end->w1, qgen);
+        /* Set gen flipped to 1, it gets reset on a cache watch operation */
+        end->w1 = xive_set_field32(END2_W1_GEN_FLIPPED, end->w1, 1);
      }
      end->w1 = xive_set_field32(END2_W1_PAGE_OFF, end->w1, qindex);
  }