[PATCH] spi: bcm2835aux: ensure interrupts are enabled for shared handler

[Rob Herring]

The BCM2835 AUX SPI has a shared interrupt line (with AUX UART).
Downstream fixes this with an AUX irqchip to demux the IRQ sources and a
DT change which breaks compatibility with older kernels. The AUX irqchip
was already rejected for upstream[1] and the DT change would break
working systems if the DTB is updated to a newer one. The latter issue
was brought to my attention by Alex Graf.

The root cause however is a bug in the shared handler. Shared handlers
must check that interrupts are actually enabled before servicing the
interrupt. Add a check that the TXEMPTY or IDLE interrupts are enabled.

[1] https://patchwork.kernel.org/patch/9781221/

Cc: Alexander Graf <agraf at suse.de>
Cc: Marc Zyngier <marc.zyngier at arm.com>
Cc: Mark Brown <broonie at kernel.org>
Cc: Eric Anholt <eric at anholt.net>
Cc: Stefan Wahren <stefan.wahren at i2se.com>
Cc: Florian Fainelli <f.fainelli at gmail.com>
Cc: Ray Jui <rjui at broadcom.com>
Cc: Scott Branden <sbranden at broadcom.com>
Cc: bcm-kernel-feedback-list at broadcom.com
Cc: linux-spi at vger.kernel.org
Cc: linux-rpi-kernel at lists.infradead.org
Cc: linux-arm-kernel at lists.infradead.org
Signed-off-by: Rob Herring <robh at kernel.org>
---
Compile tested only. I'll add something to the related github issue on 
this and hopefully someone can test and confirm.

I'm assuming the 8250 driver can handle shared irqs correctly.

Rob

 drivers/spi/spi-bcm2835aux.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/spi/spi-bcm2835aux.c b/drivers/spi/spi-bcm2835aux.c
index 1431cb98fe40..3094d818cf06 100644
--- a/drivers/spi/spi-bcm2835aux.c
+++ b/drivers/spi/spi-bcm2835aux.c
@@ -184,6 +184,11 @@ static irqreturn_t bcm2835aux_spi_interrupt(int irq, void *dev_id)
 	struct bcm2835aux_spi *bs = spi_master_get_devdata(master);
 	irqreturn_t ret = IRQ_NONE;
 
+	/* IRQ may be shared, so return if our interrupts are disabled */
+	if (!(bcm2835aux_rd(bs, BCM2835_AUX_SPI_CNTL1) &
+	      (BCM2835_AUX_SPI_CNTL1_TXEMPTY | BCM2835_AUX_SPI_CNTL1_IDLE)))
+		return ret;
+
 	/* check if we have data to read */
 	while (bs->rx_len &&
 	       (!(bcm2835aux_rd(bs, BCM2835_AUX_SPI_STAT) &
-- 
2.17.0