spi: bcm2835: enable shared interrupt support

BCM2711 shares an interrupt betweem 5 SPI interfaces (0, 3, 4, 5 & 6).
Another interrupt is shared between SPI1, SPI2 and UART1, which also
affects BCM2835/6/7. Acting on an interrupt intended for another
interface ought to be harmless (although potentially inefficient), but
it can cause this driver to crash - presumably because some critical
state is not ready.

Add a test to the spi-bcm2835 interrupt service routine that
interrupts are enabled on this interface to avoid the crash and
improve efficiency.

Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Link: https://github.com/raspberrypi/linux/issues/5048
Suggested-by: https://github.com/boe-pi
Co-developed-by: Phil Elwell <phil@raspberrypi.com>
Signed-off-by: Phil Elwell <phil@raspberrypi.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20220719105305.3076354-1-mkl@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-bcm2835.c

@@ -372,6 +372,10 @@ static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id)
 	struct bcm2835_spi *bs = dev_id;
 	u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS);
 
+	/* Bail out early if interrupts are not enabled */
+	if (!(cs & BCM2835_SPI_CS_INTR))
+		return IRQ_NONE;
+
 	/*
 	 * An interrupt is signaled either if DONE is set (TX FIFO empty)
 	 * or if RXR is set (RX FIFO >= ¾ full).
@@ -1365,8 +1369,8 @@ static int bcm2835_spi_probe(struct platform_device *pdev)
 	bcm2835_wr(bs, BCM2835_SPI_CS,
 		   BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX);
 
-	err = devm_request_irq(&pdev->dev, bs->irq, bcm2835_spi_interrupt, 0,
-			       dev_name(&pdev->dev), bs);
+	err = devm_request_irq(&pdev->dev, bs->irq, bcm2835_spi_interrupt,
+			       IRQF_SHARED, dev_name(&pdev->dev), bs);
 	if (err) {
 		dev_err(&pdev->dev, "could not request IRQ: %d\n", err);
 		goto out_dma_release;