From: Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>

The MCP23S08/17/18 SPI driver supports multiple chips sharing the same
SPI chip select by using the hardware address pins (A0-A2). Each chip
gets its own gpio_chip instance, but they all share the parent device
tree node.

Without setting gpio_chip.offset, the gpio-line-names property cannot
be used because gpiolib assigns all chips names starting at index 0.
Set offset based on cumulative GPIO count to enable sequential
gpio-line-names in device tree:

    microchip,spi-present-mask = /bits/ 8 <0x03>;  /* chips 0 and 1 */
    gpio-line-names =
        /* Chip 0: 16 names */
        "EXP0_A0", "EXP0_A1", ..., "EXP0_B7",
        /* Chip 1: 16 names */
        "EXP1_A0", "EXP1_A1", ..., "EXP1_B7";

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>
---
 drivers/pinctrl/pinctrl-mcp23s08_spi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/pinctrl/pinctrl-mcp23s08_spi.c b/drivers/pinctrl/pinctrl-mcp23s08_spi.c
index 54f61c8cb1c0..105efc85c3e7 100644
--- a/drivers/pinctrl/pinctrl-mcp23s08_spi.c
+++ b/drivers/pinctrl/pinctrl-mcp23s08_spi.c
@@ -141,6 +141,7 @@ static int mcp23s08_probe(struct spi_device *spi)
 	unsigned long spi_present_mask;
 	unsigned int ngpio = 0;
 	unsigned int addr;
+	unsigned int line_offset = 0;
 	int chips;
 	int ret;
 	u32 v;
@@ -178,6 +179,9 @@ static int mcp23s08_probe(struct spi_device *spi)
 		if (ret)
 			return ret;
 
+		data->mcp[addr]->chip.offset = line_offset;
+		line_offset += data->mcp[addr]->chip.ngpio;
+
 		data->mcp[addr]->pinctrl_desc.name = devm_kasprintf(dev, GFP_KERNEL,
 								    "mcp23xxx-pinctrl.%d",
 								    addr);

-- 
2.39.5