sfc: Use fixed-size buffers for MCDI NVRAM requests

The low-level MCDI code always uses 32-bit MMIO operations, and
callers must pad input and output buffers to multiples of 4 bytes.
The MCDI NVRAM functions are not doing this.  Also, their buffers are
declared as variable-length arrays with no explicit maximum length.

Switch to a fixed buffer size based on the chunk size used by the
MTD driver (which is a multiple of 4).

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/sfc/mtd.c b/drivers/net/sfc/mtd.c
index 3a46452..407bbad 100644
--- a/drivers/net/sfc/mtd.c
+++ b/drivers/net/sfc/mtd.c
@@ -23,7 +23,6 @@
 #include "mcdi_pcol.h"
 
 #define EFX_SPI_VERIFY_BUF_LEN 16
-#define EFX_MCDI_CHUNK_LEN 128
 
 struct efx_mtd_partition {
 	struct mtd_info mtd;
@@ -428,7 +427,7 @@
 	int rc = 0;
 
 	while (offset < end) {
-		chunk = min_t(size_t, end - offset, EFX_MCDI_CHUNK_LEN);
+		chunk = min_t(size_t, end - offset, EFX_MCDI_NVRAM_LEN_MAX);
 		rc = efx_mcdi_nvram_read(efx, part->mcdi.nvram_type, offset,
 					 buffer, chunk);
 		if (rc)
@@ -491,7 +490,7 @@
 	}
 
 	while (offset < end) {
-		chunk = min_t(size_t, end - offset, EFX_MCDI_CHUNK_LEN);
+		chunk = min_t(size_t, end - offset, EFX_MCDI_NVRAM_LEN_MAX);
 		rc = efx_mcdi_nvram_write(efx, part->mcdi.nvram_type, offset,
 					  buffer, chunk);
 		if (rc)