[PATCH] spi: xilinx: add force_irq for QSPI mode

[Vadim Fedorenko <vadfed@meta.com>]

Xilinx PG158 page 80 [1] states that master transaction inhibit bit must
be set to properly setup the transaction in QSPI mode. Add the force_irq
flag to follow this sequence.

[1] https://docs.xilinx.com/r/en-US/pg153-axi-quad-spi/Dual/Quad-SPI-Mode-Transactions

Signed-off-by: Vadim Fedorenko <vadfed@meta.com>

---
This is a follow up on the work started by Jonathan Lemon 2 years ago
and ended up nowhere.
https://lore.kernel.org/linux-spi/20210507215319.3882138-1-jonathan.lemon@gmail.com/
We still have an issue with our hardware and it would be great to fix it
in upstream driver. According to the out-of-tree driver supported by
Xilinx it's the only to work with QSPI:
https://github.com/Xilinx/linux-xlnx/blob/master/drivers/spi/spi-xilinx.c#L397

 drivers/spi/spi-xilinx.c       | 9 +++++++--
 include/linux/spi/xilinx_spi.h | 1 +
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-xilinx.c b/drivers/spi/spi-xilinx.c
index 523edfdf5dcd..9e37f3534f3f 100644
--- a/drivers/spi/spi-xilinx.c
+++ b/drivers/spi/spi-xilinx.c
@@ -83,7 +83,7 @@ struct xilinx_spi {
 	void __iomem	*regs;	/* virt. address of the control registers */
 
 	int		irq;
-
+	bool force_irq;		/* force irq to setup master inhibit */
 	u8 *rx_ptr;		/* pointer in the Tx buffer */
 	const u8 *tx_ptr;	/* pointer in the Rx buffer */
 	u8 bytes_per_word;
@@ -248,7 +248,8 @@ static int xilinx_spi_txrx_bufs(struct spi_device *spi, struct spi_transfer *t)
 	xspi->rx_ptr = t->rx_buf;
 	remaining_words = t->len / xspi->bytes_per_word;
 
-	if (xspi->irq >= 0 &&  remaining_words > xspi->buffer_size) {
+	if (xspi->irq >= 0 &&
+	    (xspi->force_irq || remaining_words > xspi->buffer_size)) {
 		u32 isr;
 		use_irq = true;
 		/* Inhibit irq to avoid spurious irqs on tx_empty*/
@@ -393,6 +394,7 @@ static int xilinx_spi_probe(struct platform_device *pdev)
 	struct resource *res;
 	int ret, num_cs = 0, bits_per_word;
 	struct spi_master *master;
+	bool force_irq = false;
 	u32 tmp;
 	u8 i;
 
@@ -400,6 +402,7 @@ static int xilinx_spi_probe(struct platform_device *pdev)
 	if (pdata) {
 		num_cs = pdata->num_chipselect;
 		bits_per_word = pdata->bits_per_word;
+		force_irq = pdata->force_irq;
 	} else {
 		of_property_read_u32(pdev->dev.of_node, "xlnx,num-ss-bits",
 					  &num_cs);
@@ -480,6 +483,8 @@ static int xilinx_spi_probe(struct platform_device *pdev)
 				dev_name(&pdev->dev), xspi);
 		if (ret)
 			goto put_master;
+
+		xspi->force_irq = force_irq;
 	}
 
 	/* SPI controller initializations */
diff --git a/include/linux/spi/xilinx_spi.h b/include/linux/spi/xilinx_spi.h
index c15d69d28e68..3934ce789d87 100644
--- a/include/linux/spi/xilinx_spi.h
+++ b/include/linux/spi/xilinx_spi.h
@@ -15,6 +15,7 @@ struct xspi_platform_data {
 	u8 bits_per_word;
 	struct spi_board_info *devices;
 	u8 num_devices;
+	bool force_irq;
 };
 
 #endif /* __LINUX_SPI_XILINX_SPI_H */
-- 
2.30.2