spi: spi-bcm2835: Fix deadlock

The bcm2835_spi_transfer_one function can create a deadlock
if it is called while another thread already has the
CCF lock.

Signed-off-by: Alexandru Tachici <alexandru.tachici@analog.com>
Fixes: f8043872e7 ("spi: add driver for BCM2835")
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20210716210245.13240-2-alexandru.tachici@analog.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-bcm2835.c

@@ -83,6 +83,7 @@ MODULE_PARM_DESC(polling_limit_us,
  * struct bcm2835_spi - BCM2835 SPI controller
  * @regs: base address of register map
  * @clk: core clock, divided to calculate serial clock
+ * @clk_hz: core clock cached speed
  * @irq: interrupt, signals TX FIFO empty or RX FIFO ¾ full
  * @tfr: SPI transfer currently processed
  * @ctlr: SPI controller reverse lookup
@@ -116,6 +117,7 @@ MODULE_PARM_DESC(polling_limit_us,
 struct bcm2835_spi {
 	void __iomem *regs;
 	struct clk *clk;
+	unsigned long clk_hz;
 	int irq;
 	struct spi_transfer *tfr;
 	struct spi_controller *ctlr;
@@ -1045,19 +1047,18 @@ static int bcm2835_spi_transfer_one(struct spi_controller *ctlr,
 {
 	struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr);
 	struct bcm2835_spidev *slv = spi_get_ctldata(spi);
-	unsigned long spi_hz, clk_hz, cdiv;
+	unsigned long spi_hz, cdiv;
 	unsigned long hz_per_byte, byte_limit;
 	u32 cs = slv->prepare_cs;
 
 	/* set clock */
 	spi_hz = tfr->speed_hz;
-	clk_hz = clk_get_rate(bs->clk);
 
-	if (spi_hz >= clk_hz / 2) {
+	if (spi_hz >= bs->clk_hz / 2) {
 		cdiv = 2; /* clk_hz/2 is the fastest we can go */
 	} else if (spi_hz) {
 		/* CDIV must be a multiple of two */
-		cdiv = DIV_ROUND_UP(clk_hz, spi_hz);
+		cdiv = DIV_ROUND_UP(bs->clk_hz, spi_hz);
 		cdiv += (cdiv % 2);
 
 		if (cdiv >= 65536)
@@ -1065,7 +1066,7 @@ static int bcm2835_spi_transfer_one(struct spi_controller *ctlr,
 	} else {
 		cdiv = 0; /* 0 is the slowest we can go */
 	}
-	tfr->effective_speed_hz = cdiv ? (clk_hz / cdiv) : (clk_hz / 65536);
+	tfr->effective_speed_hz = cdiv ? (bs->clk_hz / cdiv) : (bs->clk_hz / 65536);
 	bcm2835_wr(bs, BCM2835_SPI_CLK, cdiv);
 
 	/* handle all the 3-wire mode */
@@ -1354,6 +1355,7 @@ static int bcm2835_spi_probe(struct platform_device *pdev)
 		return bs->irq ? bs->irq : -ENODEV;
 
 	clk_prepare_enable(bs->clk);
+	bs->clk_hz = clk_get_rate(bs->clk);
 
 	err = bcm2835_dma_init(ctlr, &pdev->dev, bs);
 	if (err)