Re: [PATCH v2] powerpc/powernv: Enable PCI peer-to-peer

[Benjamin Herrenschmidt]

On Wed, 2017-07-12 at 18:01 -0500, Frederic Barrat wrote:
> > So you have the initiator refcounting in Linux and the target
> > refcounting in OPAL ... any reason for that ?
> 
> The initiator refcount is per PE and skiboot doesn't track PEs. Also 
> when the initiator refcount falls back to 0, we should restore the 
> default bypass setting for the TVE, and that's more easily done from 
> linux, since it knows the start and end address of the memory. So for 
> those reasons, I don't really have the choice, the initiator refcount 
> seems better suited in linux.
> 
> The target refcount is per PHB and it just seemed easier to keep it in opal.
> 
> Does the lack of symmetry bother you?

Only mildly. I would have put the whole refcount in Linux...

Cheers,
Ben.

Re: [PATCH v2] powerpc/powernv: Enable PCI peer-to-peer

[Frederic Barrat]

Le 12/07/2017 à 17:39, Benjamin Herrenschmidt a écrit :

On Mon, 2017-06-26 at 20:08 +0200, Frederic Barrat wrote:

+   if (desc & OPAL_PCI_P2P_ENABLE) {
+   pe_init->p2p_initiator_count++;
+   } else {
+   if (pe_init->p2p_initiator_count > 0) {
+   pe_init->p2p_initiator_count--;
+   if (!pe_init->p2p_initiator_count)
+   pnv_pci_ioda2_set_bypass(pe_init, true);
+   }


So you have the initiator refcounting in Linux and the target
refcounting in OPAL ... any reason for that ?


The initiator refcount is per PE and skiboot doesn't track PEs. Also 
when the initiator refcount falls back to 0, we should restore the 
default bypass setting for the TVE, and that's more easily done from 
linux, since it knows the start and end address of the memory. So for 
those reasons, I don't really have the choice, the initiator refcount 
seems better suited in linux.


The target refcount is per PHB and it just seemed easier to keep it in opal.

Does the lack of symmetry bother you?

  Fred

Re: [PATCH v2] powerpc/powernv: Enable PCI peer-to-peer

[Benjamin Herrenschmidt]

On Mon, 2017-06-26 at 20:08 +0200, Frederic Barrat wrote:
> +   if (desc & OPAL_PCI_P2P_ENABLE) {
> +   pe_init->p2p_initiator_count++;
> +   } else {
> +   if (pe_init->p2p_initiator_count > 0) {
> +   pe_init->p2p_initiator_count--;
> +   if (!pe_init->p2p_initiator_count)
> +   pnv_pci_ioda2_set_bypass(pe_init, true);
> +   }

So you have the initiator refcounting in Linux and the target
refcounting in OPAL ... any reason for that ?

Cheers,
Ben.

Re: [PATCH v2] powerpc/powernv: Enable PCI peer-to-peer

[Frederic Barrat]

Le 27/06/2017 à 14:32, David Laight a écrit :

From: Frederic Barrat

Sent: 26 June 2017 19:09
P9 has support for PCI peer-to-peer, enabling a device to write in the
mmio space of another device directly, without interrupting the CPU.

This patch adds support for it on powernv, by adding a new API to be
called by drivers. The pnv_pci_set_p2p(...) call configures an
'initiator', i.e the device which will issue the mmio operation, and a
'target', i.e. the device on the receiving side.

...

Two questions:

1) How does the driver get the correct address to give to the 'initiator'
in order to perform an access to the 'target'?


That's left out of this patch intentionally. The assumption is that 
there's some handshake happening between the 2 drivers. But that's an 
area where we could work to make it easier in the future.



2) Surely the API call the driver makes should be architecture neutral,
returning an error on other architectures.


The point of the patch is just to enable it on p9. I've heard of a more 
generic, on-going effort, at the PCI API level, which would be 
cross-arch. But here we just want to allow it for p9 to allow some early 
drivers to take advantage of it if they choose to.


  Fred



At least some x86 cpus also support peer-to-peer writes,
I believe they can work between cpu chips.
PCIe bridges might support them (or be configurable to support them).

David

RE: [PATCH v2] powerpc/powernv: Enable PCI peer-to-peer

[David Laight]

From: Frederic Barrat
> Sent: 26 June 2017 19:09
> P9 has support for PCI peer-to-peer, enabling a device to write in the
> mmio space of another device directly, without interrupting the CPU.
> 
> This patch adds support for it on powernv, by adding a new API to be
> called by drivers. The pnv_pci_set_p2p(...) call configures an
> 'initiator', i.e the device which will issue the mmio operation, and a
> 'target', i.e. the device on the receiving side.
...

Two questions:

1) How does the driver get the correct address to give to the 'initiator'
   in order to perform an access to the 'target'?

2) Surely the API call the driver makes should be architecture neutral,
   returning an error on other architectures.

At least some x86 cpus also support peer-to-peer writes,
I believe they can work between cpu chips.
PCIe bridges might support them (or be configurable to support them).

David

[PATCH v2] powerpc/powernv: Enable PCI peer-to-peer

[Frederic Barrat]

P9 has support for PCI peer-to-peer, enabling a device to write in the
mmio space of another device directly, without interrupting the CPU.

This patch adds support for it on powernv, by adding a new API to be
called by drivers. The pnv_pci_set_p2p(...) call configures an
'initiator', i.e the device which will issue the mmio operation, and a
'target', i.e. the device on the receiving side.

P9 really only supports mmio stores for the time being (loads are only
supported if the 2 devices are under the same PHBs), but that's
expected to change in the future, so the API allows to define both
load and store operations.

/* PCI p2p descriptor */
#define OPAL_PCI_P2P_ENABLE 0x1
#define OPAL_PCI_P2P_LOAD   0x2
#define OPAL_PCI_P2P_STORE  0x4

int pnv_pci_set_p2p(struct pci_dev *initiator, struct pci_dev *target,
   uint64_t desc)

It uses a new OPAL call, as the configuration magic is done on the
PHBs by skiboot.

Signed-off-by: Frederic Barrat 
---
Requires skiboot patch:
http://patchwork.ozlabs.org/patch/780813/

Changelog:
  - change of API
  - allow disabling of p2p setting


 arch/powerpc/include/asm/opal-api.h|  8 ++-
 arch/powerpc/include/asm/opal.h|  3 ++
 arch/powerpc/include/asm/pnv-pci.h |  2 +
 arch/powerpc/platforms/powernv/opal-wrappers.S |  1 +
 arch/powerpc/platforms/powernv/pci-ioda.c  |  3 +-
 arch/powerpc/platforms/powernv/pci.c   | 68 ++
 arch/powerpc/platforms/powernv/pci.h   |  4 ++
 7 files changed, 86 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/opal-api.h 
b/arch/powerpc/include/asm/opal-api.h
index cb3e6242a78c..2b068550b106 100644
--- a/arch/powerpc/include/asm/opal-api.h
+++ b/arch/powerpc/include/asm/opal-api.h
@@ -190,7 +190,8 @@
 #define OPAL_NPU_INIT_CONTEXT  146
 #define OPAL_NPU_DESTROY_CONTEXT   147
 #define OPAL_NPU_MAP_LPAR  148
-#define OPAL_LAST  148
+#define OPAL_PCI_SET_P2P   149
+#define OPAL_LAST  149
 
 /* Device tree flags */
 
@@ -1003,6 +1004,11 @@ enum {
XIVE_DUMP_EMU_STATE = 5,
 };
 
+/* PCI p2p descriptor */
+#define OPAL_PCI_P2P_ENABLE0x1
+#define OPAL_PCI_P2P_LOAD  0x2
+#define OPAL_PCI_P2P_STORE 0x4
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __OPAL_API_H */
diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
index 588fb1c23af9..9c099fa9bb4e 100644
--- a/arch/powerpc/include/asm/opal.h
+++ b/arch/powerpc/include/asm/opal.h
@@ -267,6 +267,9 @@ int64_t opal_xive_allocate_irq(uint32_t chip_id);
 int64_t opal_xive_free_irq(uint32_t girq);
 int64_t opal_xive_sync(uint32_t type, uint32_t id);
 int64_t opal_xive_dump(uint32_t type, uint32_t id);
+int64_t opal_pci_set_p2p(uint64_t phb_init, uint64_t phb_target,
+   uint64_t desc, uint16_t pe_number);
+
 
 /* Internal functions */
 extern int early_init_dt_scan_opal(unsigned long node, const char *uname,
diff --git a/arch/powerpc/include/asm/pnv-pci.h 
b/arch/powerpc/include/asm/pnv-pci.h
index de9681034353..59a548909d0b 100644
--- a/arch/powerpc/include/asm/pnv-pci.h
+++ b/arch/powerpc/include/asm/pnv-pci.h
@@ -26,6 +26,8 @@ extern int pnv_pci_get_presence_state(uint64_t id, uint8_t 
*state);
 extern int pnv_pci_get_power_state(uint64_t id, uint8_t *state);
 extern int pnv_pci_set_power_state(uint64_t id, uint8_t state,
   struct opal_msg *msg);
+extern int pnv_pci_set_p2p(struct pci_dev *initiator, struct pci_dev *target,
+   uint64_t desc);
 
 int pnv_phb_to_cxl_mode(struct pci_dev *dev, uint64_t mode);
 int pnv_cxl_ioda_msi_setup(struct pci_dev *dev, unsigned int hwirq,
diff --git a/arch/powerpc/platforms/powernv/opal-wrappers.S 
b/arch/powerpc/platforms/powernv/opal-wrappers.S
index f620572f891f..cf629d2d89d9 100644
--- a/arch/powerpc/platforms/powernv/opal-wrappers.S
+++ b/arch/powerpc/platforms/powernv/opal-wrappers.S
@@ -310,3 +310,4 @@ OPAL_CALL(opal_xive_dump,   OPAL_XIVE_DUMP);
 OPAL_CALL(opal_npu_init_context,   OPAL_NPU_INIT_CONTEXT);
 OPAL_CALL(opal_npu_destroy_context,OPAL_NPU_DESTROY_CONTEXT);
 OPAL_CALL(opal_npu_map_lpar,   OPAL_NPU_MAP_LPAR);
+OPAL_CALL(opal_pci_set_p2p,OPAL_PCI_SET_P2P);
diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c 
b/arch/powerpc/platforms/powernv/pci-ioda.c
index 283caf1070c9..ebb24ddf17c3 100644
--- a/arch/powerpc/platforms/powernv/pci-ioda.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
@@ -1408,7 +1408,6 @@ static int pnv_pci_vf_assign_m64(struct pci_dev *pdev, 
u16 num_vfs)
 
 static long pnv_pci_ioda2_unset_window(struct iommu_table_group *table_group,
int num);
-static void pnv_pci_ioda2_set_bypass(struct