linux-gbmc: everspin: Add Linux < 5.11 compatibility for spi_nor_read_sr

Prior to Linux 5.11, spi_nor_read_sr() was a static function defined
internally in drivers/mtd/spi-nor/core.c and was not declared in core.h.
When compiling everspin.c against Linux 5.10 (such as for Nuvoton
platforms), calls to spi_nor_read_sr() fail due to implicit function
declaration warnings treated as errors.

Add a compatibility fallback implementation of spi_nor_read_sr() for
LINUX_VERSION_CODE < KERNEL_VERSION(5, 11, 0) using spi_mem_exec_op()
when nor->spimem is valid, or nor->controller_ops->read_reg() otherwise,
matching upstream 5.10 core.c behavior.

Tested: Built a 5.10 platform image and ran on the platform. Verified that erase commands use nearly no CPU time even though they wait.

Fusion-Link: fusion2 N/A
Google-Bug-Id: 565629335
Change-Id: I13159c0c11c3c6ad4df9e5605d463bbc3649e66e
Signed-off-by: William A. Kennington III <wak@google.com>

recipes-kernel/linux/files/linux-gbmc/drivers/mtd/spi-nor/everspin.c

diff --git a/recipes-kernel/linux/files/linux-gbmc/drivers/mtd/spi-nor/everspin.c b/recipes-kernel/linux/files/linux-gbmc/drivers/mtd/spi-nor/everspin.c
index 58afbbd..58ee9eb 100644
--- a/recipes-kernel/linux/files/linux-gbmc/drivers/mtd/spi-nor/everspin.c
+++ b/recipes-kernel/linux/files/linux-gbmc/drivers/mtd/spi-nor/everspin.c
@@ -8,6 +8,25 @@
 #include <linux/version.h>
 #include "core.h"
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 11, 0)
+#include <linux/spi/spi-mem.h>
+
+static int spi_nor_read_sr(struct spi_nor *nor, u8 *sr)
+{
+	if (nor->spimem) {
+		struct spi_mem_op op =
+			SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_RDSR, 1),
+				   SPI_MEM_OP_NO_ADDR,
+				   SPI_MEM_OP_NO_DUMMY,
+				   SPI_MEM_OP_DATA_IN(1, sr, 1));
+
+		return spi_mem_exec_op(nor->spimem, &op);
+	}
+
+	return nor->controller_ops->read_reg(nor, SPINOR_OP_RDSR, sr, 1);
+}
+#endif
+
 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
 #define SNOR_ID(a, b, c) (((a) << 16) | ((b) << 8) | (c))
 #define GINFO(name, id, sec) { (name), INFO((id), 0, 64 * 1024, (sec), SECT_4K) }