[PATCH v3 08/10] pnv_phb4.c: check stack->phb not NULL in phb4_update_regions()

[Daniel Henrique Barboza <danielhb413@gmail.com>]

The last step before enabling user creatable pnv-phb4 devices still has
to do with specific XSCOM initialization code in pnv_phb4_stk_realize().

'stack->nest_regs_mr' is being init regardless of the existence of
'stack->phb', which is verified only when trying to realize the phb.
Its MemoryRegionOps,'pnv_pec_stk_nest_xscom_ops', uses
pnv_pec_stk_nest_xscom_write() as a write callback. When trying to write
the PEC_NEST_STK_BAR_EN reg, pnv_pec_stk_update_map() is called. Inside
this function, pnv_phb4_update_regions() is called twice. This function
uses stack->phb to manipulate memory regions of the phb.

When enabling user creatable phb4s, a stack that doesn't have an
associated phb (i.e. will have stack->phb = NULL) will cause a SIGINT
during boot in pnv_phb4_update_regions(). To deal with this we have
some options, including:

- check for stack->phb being not NULL in pnv_phb4_update_regions();

- change the order of the XSCOM initialization to avoid initializing
'stack->nest_regs_mr' if 'stack->phb' is NULL. This can have unintended
side-effects: there are several other regs that are being read/written
in these memory regions, and we would forbid all read/write operations
in these regs because of writes in PEC_NEST_STK_BAR_EN being problematic;

- move the XSCOM init code to phb4_realize() like the previous patch
did with 'stack->phb_regs_mr'. Besides having the same potential side
effects than the previous alternative, a lot of code would need to be
moved from pnv_phb4_pec.c to pnv_phb4.c because all the memory region
code is static.

Being the option that is less intrusive and innocus of the alternatives,
this patch keeps the XSCOM initialization as is in
pnv_phb4_stk_realize() and check for 'stack->phb' being NULL in
pnv_phb4_update_regions().

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 hw/pci-host/pnv_phb4.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/hw/pci-host/pnv_phb4.c b/hw/pci-host/pnv_phb4.c
index 152911a285..fc23a96b7f 100644
--- a/hw/pci-host/pnv_phb4.c
+++ b/hw/pci-host/pnv_phb4.c
@@ -1472,6 +1472,17 @@ void pnv_phb4_update_regions(PnvPhb4PecStack *stack)
 {
     PnvPHB4 *phb = stack->phb;
 
+    /*
+     * This will happen when there's no phb associated with the stack.
+     * pnv_pec_stk_realize() will init the nested xscom address space
+     * (stack->nest_regs_mr) that uses pnv_phb4_update_regions(), via
+     * pnv_pec_stk_update_map(), which in turn is the write callback of
+     * the PEC_NEST_STK_BAR_EN reg in pnv_pec_stk_nest_xscom_write().
+     */
+    if (!stack->phb) {
+        return;
+    }
+
     /* Unmap first always */
     if (memory_region_is_mapped(&phb->mr_regs)) {
         memory_region_del_subregion(&stack->phbbar, &phb->mr_regs);
-- 
2.33.1