[PATCH] PCI/MSI: pci-xgene-msi: Enable MSI support in ACPI boot for X-Gene v1

Hi Lorenzo,

On Thu, May 26, 2016 at 5:34 AM, Lorenzo Pieralisi
[off-list ref] wrote:

Hi Duc,

On Wed, May 25, 2016 at 04:13:35PM -0700, Duc Dang wrote:

quoted

On Thu, Feb 25, 2016 at 9:38 AM, Lorenzo Pieralisi
[off-list ref] wrote:

quoted

On Wed, Feb 24, 2016 at 02:28:10PM -0800, Duc Dang wrote:

quoted

On Wed, Feb 24, 2016 at 8:16 AM, Marc Zyngier [off-list ref] wrote:

quoted

On 24/02/16 16:09, Mark Salter wrote:

quoted

On Tue, 2016-02-09 at 17:56 -0800, Duc Dang wrote:

quoted

This patch makes pci-xgene-msi driver ACPI-aware and provides
MSI capability for X-Gene v1 PCIe controllers in ACPI boot mode.

Signed-off-by: Duc Dang <redacted>
---
 drivers/pci/host/pci-xgene-msi.c | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/host/pci-xgene-msi.c b/drivers/pci/host/pci-xgene-msi.c
index a6456b5..466aa93 100644
--- a/drivers/pci/host/pci-xgene-msi.c
+++ b/drivers/pci/host/pci-xgene-msi.c

@@ -24,6 +24,7 @@
 #include <linux/pci.h>
 #include <linux/platform_device.h>
 #include <linux/of_pci.h>
+#include <linux/acpi.h>

 #define MSI_IR0                     0x000000
 #define MSI_INT0            0x800000

@@ -39,7 +40,7 @@ struct xgene_msi_group {
 };

 struct xgene_msi {
-    struct device_node      *node;
+    struct fwnode_handle    *fwnode;
     struct irq_domain       *inner_domain;
     struct irq_domain       *msi_domain;
     u64                     msi_addr;

@@ -249,6 +250,13 @@ static const struct irq_domain_ops msi_domain_ops = {
     .free   = xgene_irq_domain_free,
 };

+#ifdef CONFIG_ACPI
+static struct fwnode_handle *xgene_msi_get_fwnode(struct device *dev)
+{
+    return xgene_msi_ctrl.fwnode;
+}
+#endif
+
 static int xgene_allocate_domains(struct xgene_msi *msi)
 {
     msi->inner_domain = irq_domain_add_linear(NULL, NR_MSI_VEC,

@@ -256,7 +264,7 @@ static int xgene_allocate_domains(struct xgene_msi *msi)
     if (!msi->inner_domain)
             return -ENOMEM;

-    msi->msi_domain = pci_msi_create_irq_domain(of_node_to_fwnode(msi->node),
+    msi->msi_domain = pci_msi_create_irq_domain(msi->fwnode,
                                                 &xgene_msi_domain_info,
                                                 msi->inner_domain);

This doesn't work for me (ACPI probing on Mustang) unless I change this
to be pci_msi_create_default_irq_domain(). The problem seems to be that
the MSI probe happens after the PCIe RC is probed so there is no MSI domain
at the time the PCIe root is initialized by ACPI.

pci_msi_create_default_irq_domain is the wrong thing do use, specially
if you have multiple MSI controllers in the system. I certainly wouldn't
want to see it being used on arm64.

This is the usual dependency hell. You try moving the probing earlier,
but that may break something else in the process.

Hi Mark and Marc,

I have modified Tianocore firmware to have MSI node declared before
PCIe node in Dsdt table. With this modification, the MSI driver will
be loaded before PCIe driver and MSI domain is available at the time
PCIe root is initialized.

I am totally against this. We should not hack ACPI tables to make
the kernel work (on top of that with unwritten ordering rules that may
well require changes as kernel evolves), we should have a standard set
of bindings that people use to describe HW in the DSDT and the kernel(s)
has to cope with that. If there is a dependency problem in the description
we may solve it at bindings level, but I absolutely do not want to rely
on DSDT nodes ordering for things to work, that's fragile, no shortcuts
please.

Hi Lorenzo, Bjorn,

(Refresh this thread on this merge cycle)

I tried to use _DEP method to describe the dependency of PCIe node to
MSI node but it turns out that PCIe driver does not check for the
dependency (only EC (ec.c) and I2C core (i2c-core.c) use
acpi_walk_dep_device_list to check for dependency before loading
dependent drivers)

Do you have other suggestion/example about how to ensure strict
ordering on driver loading in ACPI boot mode without changing the
order of ACPI nodes in DSDT?

Before doing anything else, I would like to ask you to report the code
paths leading to failures (what fails actually ?) please, and I want
to understand what "this does not work" means.

In particular:

- Why using pci_msi_create_default_irq_domain() works
- Why, if you change the DSDT nodes ordering, things work (please add
  some debugging to MSI allocation functions to detect the code paths
  leading to correct MSI allocation)
- What's the difference wrt the DT probe path

The MSI allocation happens with following code path (I use PMC pm80xx
SAS driver as an example (drivers/scsi/pm8001/pm8001_init.c)):
pci_enable_msix_exact
    pci_enable_msix_range
        pci_enable_msix
            msix_capbility_init
                pci_msi_setup_msi_irqs
                    pci_msi_get_domain
                        dev_get_msi_domain
                        arch_get_pci_msi_domain
                            return pci_msi_default_domain;

In my failing case: pci_msi_get_domain return NULL, so MSI allocation
function (pci_enable_msix_exact) fails.

The expected MSI domain is registered when X-Gene MSI driver is
initialized and is attached to each PCI bus by calling
pci_set_bus_msi_domain during PCIe bus-scan:
pci_scan_root_bus
    pci_scan_root_bus_msi
        pci_scan_child_bus
            pci_scan_bridge
                pci_add_new_bus
                    pci_alloc_child_bus
                        pci_set_bus_msi_domain
                            pci_host_bridge_msi_domain
                                pci_host_bridge_of_msi_domain
                                pci_host_bridge_acpi_msi_domain

+ When booting with DT: X-Gene MSI driver is initialized early
(subsys_initcall level); X-Gene PCIe driver is initialized later at
device_initcall level (using module_platform_driver). Because of that
when PCIe enumeration happens, the X-Gene MSI domain was already
registered and available. So when the driver of PCIe Endpoint devices
gets loaded, the call to pci_enable_msix_exact (to allocate MSI)
succeeds.

+ When booting with ACPI: acpi_scan_init is called at subsys_initcall
level (the same level with X-Gene MSI driver):
acpi_init
    acpi_bus_init (GIC is initialized here)
        acpi_scan_init
            acpi_pci_root_init
            acpi_pci_link_init
            ...
            acpi_bus_scan
                acpi_bus_check_add
 ...

Currently, in DSDT table, X-Gene MSI node is defined right after
X-Gene PCIe nodes. So PCIe driver initialization and PCIe enumeration
happens before MSI driver is initialized. During PCIe bus scan, the
pci_set_bus_msi_domain gets a NULL  irq_domain value from
pci_host_bridge_msi_domain (as MSI driver is not initialized), so
there is no MSI support for PCIe bus.

+ Using pci_msi_create_default_irq_domain() helps MSI allocation
succeed as pci_msi_get_domain (in the code path of
pci_enable_msix_exact above) can fall back to get a valid domain from
arch_get_pci_msi_domain (please note that PCIe endpoint driver gets
called later (at device_initcall level (using module_init)), so at the
time PCIe endpoint driver probe function executes, the MSI driver
already register the global MSI domain with
pci_msi_create_default_irq_domain)

+ If changing DSDT node ordering, to define MSI node before PCIe
nodes, then X-Gene MSI driver will be loaded before PCIe host driver.
At the time PCIe enumeration happens, X-Gene MSI driver already
registered a valid MSI domain (by calling
pci_msi_register_fwnode_provider to register the fwnode provider
function), so all the detected PCIe buses (and PCIe endpoint devices)
will have a valid MSI domain attached to them (as a result of function
pci_set_bus_msi_domain)

Regards,
Duc Dang.

When we have a detailed view of MSI allocation code paths and failures
we can see what we can do to fix it in ACPI.

Thanks,
Lorenzo