PCI: mediatek: Fix operator precedence in PCIE_FTS_NUM_L0 macro

[ Upstream commit 282305d ]

The original PCIE_FTS_NUM_L0(x) macro was buggy due to improper operator
precedence, where ((x) & 0xff << 8) was evaluated as ((x) & 0xff00).

Instead of just fixing the parentheses, use the standard FIELD_PREP()
macro. This makes the code more robust by automatically handling masks
and shifts, while also adding compile-time type and range checking to
ensure the value fits within PCIE_FTS_NUM_MASK.

Fixes: 637cfac ("PCI: mediatek: Add MediaTek PCIe host controller support")
Signed-off-by: Li RongQing <lirongqing@baidu.com>
[mani: added the bitfield header include spotted by Sashiko]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Link: https://patch.msgid.link/20260515005552.2343-1-lirongqing@baidu.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: lrq-max

drivers/pci/controller/pcie-mediatek.c

@@ -7,6 +7,7 @@
  *	   Honghui Zhang <honghui.zhang@mediatek.com>
  */
 
+#include <linux/bitfield.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/iopoll.h>
@@ -60,7 +61,7 @@
 /* MediaTek specific configuration registers */
 #define PCIE_FTS_NUM		0x70c
 #define PCIE_FTS_NUM_MASK	GENMASK(15, 8)
-#define PCIE_FTS_NUM_L0(x)	((x) & 0xff << 8)
+#define PCIE_FTS_NUM_L0(x)	FIELD_PREP(PCIE_FTS_NUM_MASK, x)
 
 #define PCIE_FC_CREDIT		0x73c
 #define PCIE_FC_CREDIT_MASK	(GENMASK(31, 31) | GENMASK(28, 16))