Re: [PATCH 4/4] ppc/xive: Add support for the PC MMIOs

[Frederic Barrat]

On 29/08/2023 16:32, Cédric Le Goater wrote:

The XIVE interrupt contoller maintains various fields on interrupt
targets in a structure called NVT. Each unit has a NVT cache, backed
by RAM.

When the NVT structure is not local (in RAM) to the chip, the XIVE
interrupt controller forwards the memory operation to the owning chip
using the PC MMIO region configured for this purpose. QEMU does not
need to be so precise since software shouldn't perform any of these
operations. The model implementation is simplified to return the RAM
address of the NVT structure which is then used by pnv_xive_vst_write
or read to perform the operation in RAM.

Remove the last use of pnv_xive_get_remote().

Signed-off-by: Cédric Le Goater <c...@kaod.org>
-

Nice cleanup

Reviewed-by: Frederic Barrat <fbar...@linux.ibm.com>

  Fred

  hw/intc/pnv_xive.c | 84 ++++++++++++++++++++++++++--------------------
  1 file changed, 48 insertions(+), 36 deletions(-)

diff --git a/hw/intc/pnv_xive.c b/hw/intc/pnv_xive.c
index aae5cb6f607b..9b10e905195a 100644
--- a/hw/intc/pnv_xive.c
+++ b/hw/intc/pnv_xive.c
@@ -84,28 +84,6 @@ static uint8_t pnv_xive_block_id(PnvXive *xive)
      return blk;
  }

-/*

- * Remote access to controllers. HW uses MMIOs. For now, a simple scan
- * of the chips is good enough.
- *
- * TODO: Block scope support
- */
-static PnvXive *pnv_xive_get_remote(uint8_t blk)
-{
-    PnvMachineState *pnv = PNV_MACHINE(qdev_get_machine());
-    int i;
-
-    for (i = 0; i < pnv->num_chips; i++) {
-        Pnv9Chip *chip9 = PNV9_CHIP(pnv->chips[i]);
-        PnvXive *xive = &chip9->xive;
-
-        if (pnv_xive_block_id(xive) == blk) {
-            return xive;
-        }
-    }
-    return NULL;
-}
-
  /*
   * VST accessors for SBE, EAT, ENDT, NVT
   *
@@ -209,6 +187,42 @@ static uint64_t pnv_xive_vst_addr_indirect(PnvXive *xive, 
uint32_t type,
      return pnv_xive_vst_addr_direct(xive, type, vsd, (idx % vst_per_page));
  }

+/*

+ * This is a simplified model of operation forwarding on a remote IC.
+ *
+ * A PC MMIO address is built to identify the NVT structure. The load
+ * on the remote IC will return the address of the structure in RAM,
+ * which will then be used by pnv_xive_vst_write/read to perform the
+ * RAM operation.
+ */
+static uint64_t pnv_xive_vst_addr_remote(PnvXive *xive, uint32_t type,
+                                         uint64_t vsd, uint8_t blk,
+                                         uint32_t idx)
+{
+    const XiveVstInfo *info = &vst_infos[type];
+    uint64_t remote_addr = vsd & VSD_ADDRESS_MASK;
+    uint64_t vst_addr;
+    MemTxResult result;
+
+    if (type != VST_TSEL_VPDT) {
+        xive_error(xive, "VST: invalid access on remote VST %s %x/%x !?",
+                   info->name, blk, idx);
+        return 0;
+    }
+
+    remote_addr |= idx << xive->pc_shift;
+
+    vst_addr = address_space_ldq_be(&address_space_memory, remote_addr,
+                                    MEMTXATTRS_UNSPECIFIED, &result);
+    if (result != MEMTX_OK) {
+        xive_error(xive, "VST: read failed at @0x%"  HWADDR_PRIx
+                   " for NVT %x/%x\n", remote_addr, blk, idx);
+        return 0;
+    }
+
+    return vst_addr;
+}
+
  static uint64_t pnv_xive_vst_addr(PnvXive *xive, uint32_t type, uint8_t blk,
                                    uint32_t idx)
  {
@@ -225,14 +239,7 @@ static uint64_t pnv_xive_vst_addr(PnvXive *xive, uint32_t 
type, uint8_t blk,

/* Remote VST access */

      if (GETFIELD(VSD_MODE, vsd) == VSD_MODE_FORWARD) {
-        if (type != VST_TSEL_VPDT) {
-            xive_error(xive, "VST: invalid access on remote VST %s %x/%x !?",
-                       info->name, blk, idx);
-            return 0;
-        }
-        xive = pnv_xive_get_remote(blk);
-
-        return xive ? pnv_xive_vst_addr(xive, type, blk, idx) : 0;
+        return pnv_xive_vst_addr_remote(xive, type, vsd, blk, idx);
      }

if (VSD_INDIRECT & vsd) {

@@ -1785,16 +1792,20 @@ static const MemoryRegionOps pnv_xive_vc_ops = {
  };

/*

- * Presenter Controller MMIO region. The Virtualization Controller
- * updates the IPB in the NVT table when required. Not modeled.
+ * Presenter Controller MMIO region. Points to the NVT sets.
+ *
+ * HW implements all possible mem ops to the underlying NVT structure
+ * but QEMU does not need to be so precise. The model implementation
+ * simply returns the RAM address of the NVT structure which is then
+ * used by pnv_xive_vst_write/read to perform the RAM operation.
   */
-static uint64_t pnv_xive_pc_read(void *opaque, hwaddr addr,
-                                 unsigned size)
+static uint64_t pnv_xive_pc_read(void *opaque, hwaddr offset, unsigned size)
  {
      PnvXive *xive = PNV_XIVE(opaque);
+    uint32_t nvt_idx = offset >> xive->pc_shift;
+    uint8_t blk = pnv_xive_block_id(xive); /* TODO: VDT -> block xlate */

- xive_error(xive, "PC: invalid read @%"HWADDR_PRIx, addr);

-    return -1;
+    return pnv_xive_vst_addr(xive, VST_TSEL_VPDT, blk, nvt_idx);
  }

static void pnv_xive_pc_write(void *opaque, hwaddr addr,

@@ -2016,6 +2027,7 @@ static void pnv_xive_realize(DeviceState *dev, Error 
**errp)
      /* Presenter Controller MMIO region (not modeled) */
      memory_region_init_io(&xive->pc_mmio, OBJECT(xive), &pnv_xive_pc_ops, 
xive,
                            "xive-pc", PNV9_XIVE_PC_SIZE);
+    xive->pc_mmio.disable_reentrancy_guard = true;

/* Thread Interrupt Management Area (Direct) */

      memory_region_init_io(&xive->tm_mmio, OBJECT(xive), &pnv_xive_tm_ops,