selftests/powerpc: Use req_max_processed_len from sysfs NX capabilities

On PowerVM, the hypervisor defines the maximum buffer length for
each NX request and the kernel exported this value via sysfs.

This patch reads this value if the sysfs entry is available and
is used to limit the request length.

Signed-off-by: Haren Myneni <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

tools/testing/selftests/powerpc/nx-gzip/Makefile

···
-CFLAGS = -O3 -m64 -I./include
+CFLAGS = -O3 -m64 -I./include -I../include
 
 TEST_GEN_FILES := gzfht_test gunz_test
 TEST_PROGS := nx-gzip-test.sh
 
 include ../../lib.mk
 
-$(TEST_GEN_FILES): gzip_vas.c
+$(TEST_GEN_FILES): gzip_vas.c ../utils.c

tools/testing/selftests/powerpc/nx-gzip/gzfht_test.c

···
 #include <assert.h>
 #include <errno.h>
 #include <signal.h>
+#include "utils.h"
 #include "nxu.h"
 #include "nx.h"
 
···
 #define NX_MIN(X, Y) (((X) < (Y)) ? (X) : (Y))
 #define FNAME_MAX 1024
 #define FEXT ".nx.gz"
+
+#define SYSFS_MAX_REQ_BUF_PATH "devices/vio/ibm,compression-v1/nx_gzip_caps/req_max_processed_len"
 
 /*
  * LZ counts returned in the user supplied nx_gzip_crb_cpb_t structure.
···
 	struct nx_gzip_crb_cpb_t *cmdp;
 	uint32_t pagelen = 65536;
 	int fault_tries = NX_MAX_FAULTS;
+	char buf[32];
 
 	cmdp = (void *)(uintptr_t)
 		aligned_alloc(sizeof(struct nx_gzip_crb_cpb_t),
···
 	assert(NULL != (outbuf = (char *)malloc(outlen)));
 	nxu_touch_pages(outbuf, outlen, pagelen, 1);
 
-	/* Compress piecemeal in smallish chunks */
-	chunk = 1<<22;
+	/*
+	 * On PowerVM, the hypervisor defines the maximum request buffer
+	 * size is defined and this value is available via sysfs.
+	 */
+	if (!read_sysfs_file(SYSFS_MAX_REQ_BUF_PATH, buf, sizeof(buf))) {
+		chunk = atoi(buf);
+	} else {
+		/* sysfs entry is not available on PowerNV */
+		/* Compress piecemeal in smallish chunks */
+		chunk = 1<<22;
+	}
 
 	/* Write the gzip header to the stream */
 	num_hdr_bytes = gzip_header_blank(outbuf);