spi: spi-mem: Protect dirmap_create() with spi_mem_access_start/end

spi_mem_dirmap_create() may reconfigure controller-wide settings,
which can interfere with concurrent transfers to other devices
sharing the same SPI controller but using different chip selects.

Wrap the ->dirmap_create() callback with spi_mem_access_start() and
spi_mem_access_end() to serialize access and prevent cross-CS
interference during dirmap creation.

This patch has been verified on a setup where a SPI TPM is connected
to CS0 of a SPI controller, while a SPI NOR flash is connected to CS1
of the same controller. Without this patch, spi_mem_dirmap_create()
for the SPI NOR flash interferes with ongoing SPI TPM data transfers,
resulting in failure to create the TPM device. This was tested on an
ASPEED AST2700 EVB.

Signed-off-by: Chin-Ting Kuo <chin-ting_kuo@aspeedtech.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Link: https://patch.msgid.link/20260120123005.1392071-2-chin-ting_kuo@aspeedtech.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: chintingkuo

drivers/spi/spi-mem.c

@@ -708,9 +708,18 @@ spi_mem_dirmap_create(struct spi_mem *mem,
 
 	desc->mem = mem;
 	desc->info = *info;
-	if (ctlr->mem_ops && ctlr->mem_ops->dirmap_create)
+	if (ctlr->mem_ops && ctlr->mem_ops->dirmap_create) {
+		ret = spi_mem_access_start(mem);
+		if (ret) {
+			kfree(desc);
+			return ERR_PTR(ret);
+		}
+
 		ret = ctlr->mem_ops->dirmap_create(desc);
 
+		spi_mem_access_end(mem);
+	}
+
 	if (ret) {
 		desc->nodirmap = true;
 		if (!spi_mem_supports_op(desc->mem, &desc->info.op_tmpl))