powerpc/powernv: Document cxl dependency on special case in pnv_eeh_reset()

pnv_eeh_reset() has special handling for PEs whose primary bus is the
root bus or the bus immediately underneath the root port.

The cxl bi-modal card support added in b0b5e5918ad1 ("cxl: Add
cxl_check_and_switch_mode() API to switch bi-modal cards") relies on
this behaviour when hot-resetting the CAPI adapter following a mode
switch.  Document this in pnv_eeh_reset() so we don't accidentally break
it.

Suggested-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/platforms/powernv/eeh-powernv.c b/arch/powerpc/platforms/powernv/eeh-powernv.c
index 6fb5522acd7085c3ffdd003e84637050dcb92146..d2f19821d71dbae2d749d0baaed56d4d9d570570 100644 (file)
--- a/arch/powerpc/platforms/powernv/eeh-powernv.c
+++ b/arch/powerpc/platforms/powernv/eeh-powernv.c
@@ -1102,6 +1102,13 @@ static int pnv_eeh_reset(struct eeh_pe *pe, int option)
                return -EIO;
        }
 
+       /*
+        * If dealing with the root bus (or the bus underneath the
+        * root port), we reset the bus underneath the root port.
+        *
+        * The cxl driver depends on this behaviour for bi-modal card
+        * switching.
+        */
        if (pci_is_root_bus(bus) ||
            pci_is_root_bus(bus->parent))
                return pnv_eeh_root_reset(hose, option);