Re: [PATCHv3 2/2] pseries/scm: buffer pmem's bound addr in dt for kexec kernel

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

On 3/4/20 2:17 PM, Pingfan Liu wrote:
> 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.
> 


that should be fixed by

faa6d21153fd11e139dd880044521389b34a24f2
Author:       Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
AuthorDate:   Tue Sep 3 18:04:52 2019 +0530
Commit:       Michael Ellerman <mpe@ellerman.id.au>
CommitDate:   Wed Sep 25 08:32:59 2019 +1000

powerpc/nvdimm: use H_SCM_QUERY hcall on H_OVERLAP error

Right now we force an unbind of SCM memory at drcindex on H_OVERLAP error.
This really slows down operations like kexec where we get the H_OVERLAP
error because we don't go through a full hypervisor re init.

H_OVERLAP error for a H_SCM_BIND_MEM hcall indicates that SCM memory at
drc index is already bound. Since we don't specify a logical memory
address for bind hcall, we can use the H_SCM_QUERY hcall to query
the already bound logical address.




> 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'.
> 

-aneesh