powerpc/papr_scm: Implement support for H_SCM_FLUSH hcall

Add support for ND_REGION_ASYNC capability if the device tree
indicates 'ibm,hcall-flush-required' property in the NVDIMM node.
Flush is done by issuing H_SCM_FLUSH hcall to the hypervisor.

If the flush request failed, the hypervisor is expected to
to reflect the problem in the subsequent nvdimm H_SCM_HEALTH call.

This patch prevents mmap of namespaces with MAP_SYNC flag if the
nvdimm requires an explicit flush[1].

References:
[1] https://github.com/avocado-framework-tests/avocado-misc-tests/blob/master/memory/ndctl.py.data/map_sync.c

Signed-off-by: Shivaprasad G Bhat <[e-mail]>
Reviewed-by: Aneesh Kumar K.V <[e-mail]>
[mpe: Use unsigned long / long instead of uint64_t/int64_t]
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/161703936121.36.7260632399582101498.stgit@e1fbed493c87

Documentation/powerpc/papr_hcalls.rst

···
 Given a DRC Index collect the performance statistics for NVDIMM and copy them
 to the resultBuffer.
 
+**H_SCM_FLUSH**
+
+| Input: *drcIndex, continue-token*
+| Out: *continue-token*
+| Return Value: *H_SUCCESS, H_Parameter, H_P2, H_BUSY*
+
+Given a DRC Index Flush the data to backend NVDIMM device.
+
+The hcall returns H_BUSY when the flush takes longer time and the hcall needs
+to be issued multiple times in order to be completely serviced. The
+*continue-token* from the output to be passed in the argument list of
+subsequent hcalls to the hypervisor until the hcall is completely serviced
+at which point H_SUCCESS or other error is returned by the hypervisor.
+
 References
 ==========
 .. [1] "Power Architecture Platform Reference"

arch/powerpc/include/asm/hvcall.h

···
 #define H_SCM_HEALTH            0x400
 #define H_SCM_PERFORMANCE_STATS 0x418
 #define H_RPT_INVALIDATE	0x448
-#define MAX_HCALL_OPCODE	H_RPT_INVALIDATE
+#define H_SCM_FLUSH		0x44C
+#define MAX_HCALL_OPCODE	H_SCM_FLUSH
 
 /* Scope args for H_SCM_UNBIND_ALL */
 #define H_UNBIND_SCOPE_ALL (0x1)

arch/powerpc/platforms/pseries/papr_scm.c

···
 	uint64_t block_size;
 	int metadata_size;
 	bool is_volatile;
+	bool hcall_flush_required;
 
 	uint64_t bound_addr;
 
···
 	/* length of the stat buffer as expected by phyp */
 	size_t stat_buffer_len;
 };
+
+static int papr_scm_pmem_flush(struct nd_region *nd_region,
+			       struct bio *bio __maybe_unused)
+{
+	struct papr_scm_priv *p = nd_region_provider_data(nd_region);
+	unsigned long ret_buf[PLPAR_HCALL_BUFSIZE], token = 0;
+	long rc;
+
+	dev_dbg(&p->pdev->dev, "flush drc 0x%x", p->drc_index);
+
+	do {
+		rc = plpar_hcall(H_SCM_FLUSH, ret_buf, p->drc_index, token);
+		token = ret_buf[0];
+
+		/* Check if we are stalled for some time */
+		if (H_IS_LONG_BUSY(rc)) {
+			msleep(get_longbusy_msecs(rc));
+			rc = H_BUSY;
+		} else if (rc == H_BUSY) {
+			cond_resched();
+		}
+	} while (rc == H_BUSY);
+
+	if (rc) {
+		dev_err(&p->pdev->dev, "flush error: %lld", rc);
+		rc = -EIO;
+	} else {
+		dev_dbg(&p->pdev->dev, "flush drc 0x%x complete", p->drc_index);
+	}
+
+	return rc;
+}
 
 static LIST_HEAD(papr_nd_regions);
 static DEFINE_MUTEX(papr_ndr_lock);
···
 	ndr_desc.num_mappings = 1;
 	ndr_desc.nd_set = &p->nd_set;
 
+	if (p->hcall_flush_required) {
+		set_bit(ND_REGION_ASYNC, &ndr_desc.flags);
+		ndr_desc.flush = papr_scm_pmem_flush;
+	}
+
 	if (p->is_volatile)
 		p->region = nvdimm_volatile_region_create(p->bus, &ndr_desc);
 	else {
···
 	p->block_size = block_size;
 	p->blocks = blocks;
 	p->is_volatile = !of_property_read_bool(dn, "ibm,cache-flush-required");
+	p->hcall_flush_required = of_property_read_bool(dn, "ibm,hcall-flush-required");
 
 	/* We just need to ensure that set cookies are unique across */
 	uuid_parse(uuid_str, (uuid_t *) uuid);