Appreciate for your kind review. And I have some comment as below.

On Fri, Mar 13, 2020 at 11:18 AM Oliver O'Halloran [off-list ref] wrote:

On Wed, Mar 4, 2020 at 7:50 PM Pingfan Liu [off-list ref] wrote:

quoted

At present, plpar_hcall(H_SCM_BIND_MEM, ...) takes a very long time, so
if dumping to fsdax, it will take a very long time.

Take a closer look, during the papr_scm initialization, the only
configuration is through drc_pmem_bind()-> plpar_hcall(H_SCM_BIND_MEM,
...), which helps to set up the bound address.

On pseries, for kexec -l/-p kernel, there is no reset of hardware, and this
step can be stepped around to save times.  So the pmem bound address can be
passed to the 2nd kernel through a dynamic added property "bound-addr" in
dt node 'ibm,pmemory'.

Signed-off-by: Pingfan Liu <redacted>
To: linuxppc-dev@lists.ozlabs.org
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Aneesh Kumar K.V <redacted>
Cc: Oliver O'Halloran <oohall@gmail.com>
Cc: Dan Williams <redacted>
Cc: Andrew Donnellan <redacted>
Cc: Christophe Leroy <redacted>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <redacted>
Cc: kexec@lists.infradead.org
---
note: This patch has not been tested since I can not get such a pseries with pmem.
      Please kindly to give some suggestion, thanks.

There was some qemu patches to implement the Hcall interface floating
around a while ago. I'm not sure they ever made it into upstream qemu
though.

Unfortunately, it does not appear in latest qemu code. I think
probably virt-pmem has achieved the same feature.

quoted

---
 arch/powerpc/platforms/pseries/of_helpers.c |  1 +
 arch/powerpc/platforms/pseries/papr_scm.c   | 33 ++++++++++++++++++++---------
 drivers/of/base.c                           |  1 +
 3 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/of_helpers.c b/arch/powerpc/platforms/pseries/of_helpers.c
index 1022e0f..2c7bab4 100644
--- a/arch/powerpc/platforms/pseries/of_helpers.c
+++ b/arch/powerpc/platforms/pseries/of_helpers.c

@@ -34,6 +34,7 @@ struct property *new_property(const char *name, const int length,
        kfree(new);
        return NULL;
 }
+EXPORT_SYMBOL(new_property);

 /**
  * pseries_of_derive_parent - basically like dirname(1)

diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
index 0b4467e..54ae903 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/arch/powerpc/platforms/pseries/papr_scm.c

@@ -14,6 +14,7 @@
 #include <linux/delay.h>

 #include <asm/plpar_wrappers.h>
+#include "of_helpers.h"

 #define BIND_ANY_ADDR (~0ul)

@@ -383,7 +384,7 @@ static int papr_scm_probe(struct platform_device *pdev)
 {
        struct device_node *dn = pdev->dev.of_node;
        u32 drc_index, metadata_size;
-       u64 blocks, block_size;
+       u64 blocks, block_size, bound_addr = 0;
        struct papr_scm_priv *p;
        const char *uuid_str;
        u64 uuid[2];

@@ -440,17 +441,29 @@ static int papr_scm_probe(struct platform_device *pdev)
        p->metadata_size = metadata_size;
        p->pdev = pdev;

-       /* request the hypervisor to bind this region to somewhere in memory */
-       rc = drc_pmem_bind(p);
+       of_property_read_u64(dn, "bound-addr", &bound_addr);
+       if (bound_addr) {
+               p->bound_addr = bound_addr;
+       } else {
+               struct property *property;
+               u64 big;

-       /* If phyp says drc memory still bound then force unbound and retry */
-       if (rc == H_OVERLAP)
-               rc = drc_pmem_query_n_bind(p);
+               /* request the hypervisor to bind this region to somewhere in memory */
+               rc = drc_pmem_bind(p);

-       if (rc != H_SUCCESS) {
-               dev_err(&p->pdev->dev, "bind err: %d\n", rc);
-               rc = -ENXIO;
-               goto err;
+               /* If phyp says drc memory still bound then force unbound and retry */
+               if (rc == H_OVERLAP)
+                       rc = drc_pmem_query_n_bind(p);
+
+               if (rc != H_SUCCESS) {
+                       dev_err(&p->pdev->dev, "bind err: %d\n", rc);
+                       rc = -ENXIO;
+                       goto err;
+               }
+               big = cpu_to_be64(p->bound_addr);
+               property = new_property("bound-addr", sizeof(u64), (const unsigned char *)&big,
+                       NULL);

That should probably be "linux,bound-addr"

OK, thanks for suggestion.

The other thing that stands out to me is that you aren't removing the

Yes, you are right. I will fix it in V2.

property when the region is unbound. As a general rule I'd prefer we
didn't hack the DT at runtime, but if we are going to then we should
make sure we're not putting anything wrong in there.

Actually, the dynamically building of DT is widely used by "kexec -l".

The pre-condition for the hacked method is that the bound pmem-addr
will not change. And on pseries, during kexec -l/-p, a machine reset
will not be invoked, so the bound address should be changed.

Thanks,
Pingfan
[...]