spi: spi-ti-qspi: Fix a bug when accessing non default CS

When switching ChipSelect from default CS0 to any other CS, driver fails
to update the bits in system control module register that control which
CS is mapped for MMIO access. This causes reads to fail when driver
tries to access QSPI flash on CS1/2/3.

Fix this by updating appropriate bits whenever active CS changes.

Reported-by: Andreas Dannenberg <dannenberg@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20191211155216.30212-1-vigneshr@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-ti-qspi.c

@@ -62,6 +62,7 @@ struct ti_qspi {
 	u32 dc;
 
 	bool mmap_enabled;
+	int current_cs;
 };
 
 #define QSPI_PID			(0x0)
@@ -487,6 +488,7 @@ static void ti_qspi_enable_memory_map(struct spi_device *spi)
 				   MEM_CS_EN(spi->chip_select));
 	}
 	qspi->mmap_enabled = true;
+	qspi->current_cs = spi->chip_select;
 }
 
 static void ti_qspi_disable_memory_map(struct spi_device *spi)
@@ -498,6 +500,7 @@ static void ti_qspi_disable_memory_map(struct spi_device *spi)
 		regmap_update_bits(qspi->ctrl_base, qspi->ctrl_reg,
 				   MEM_CS_MASK, 0);
 	qspi->mmap_enabled = false;
+	qspi->current_cs = -1;
 }
 
 static void ti_qspi_setup_mmap_read(struct spi_device *spi, u8 opcode,
@@ -543,7 +546,7 @@ static int ti_qspi_exec_mem_op(struct spi_mem *mem,
 
 	mutex_lock(&qspi->list_lock);
 
-	if (!qspi->mmap_enabled)
+	if (!qspi->mmap_enabled || qspi->current_cs != mem->spi->chip_select)
 		ti_qspi_enable_memory_map(mem->spi);
 	ti_qspi_setup_mmap_read(mem->spi, op->cmd.opcode, op->data.buswidth,
 				op->addr.nbytes, op->dummy.nbytes);
@@ -799,6 +802,7 @@ no_dma:
 		}
 	}
 	qspi->mmap_enabled = false;
+	qspi->current_cs = -1;
 
 	ret = devm_spi_register_master(&pdev->dev, master);
 	if (!ret)