[PATCH v3 2/2] spi: rockchip: Disable Runtime PM when chip select is asserted

[Jeffy Chen <jeffy.chen@rock-chips.com>]

The rockchip spi would stop driving pins when runtime suspended, which
might break slave's xfer(for example cros_ec).

Since we have pullups on those pins, we only need to care about this
when the CS asserted.

So let's keep the spi alive when chip select is asserted.

Also use pm_runtime_put instead of pm_runtime_put_sync.

Suggested-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>

---

Changes in v3:
Store cs states in struct rockchip_spi, and use it to detect cs state
instead of hw register.

Changes in v2:
Improve commit message and comments and coding style.

 drivers/spi/spi-rockchip.c | 51 +++++++++++++++++++++++-----------------------
 1 file changed, 26 insertions(+), 25 deletions(-)

diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
index 52ea160..0b4a52b 100644
--- a/drivers/spi/spi-rockchip.c
+++ b/drivers/spi/spi-rockchip.c
@@ -25,6 +25,11 @@
 
 #define DRIVER_NAME "rockchip-spi"
 
+#define ROCKCHIP_SPI_CLR_BITS(reg, bits) \
+		writel_relaxed(readl_relaxed(reg) & ~(bits), reg)
+#define ROCKCHIP_SPI_SET_BITS(reg, bits) \
+		writel_relaxed(readl_relaxed(reg) | (bits), reg)
+
 /* SPI register offsets */
 #define ROCKCHIP_SPI_CTRLR0			0x0000
 #define ROCKCHIP_SPI_CTRLR1			0x0004
@@ -149,6 +154,8 @@
  */
 #define ROCKCHIP_SPI_MAX_TRANLEN		0xffff
 
+#define ROCKCHIP_SPI_MAX_CS_NUM			2
+
 enum rockchip_ssi_type {
 	SSI_MOTO_SPI = 0,
 	SSI_TI_SSP,
@@ -193,6 +200,8 @@ struct rockchip_spi {
 	/* protect state */
 	spinlock_t lock;
 
+	bool cs_asserted[ROCKCHIP_SPI_MAX_CS_NUM];
+
 	u32 use_dma;
 	struct sg_table tx_sg;
 	struct sg_table rx_sg;
@@ -264,37 +273,29 @@ static inline u32 rx_max(struct rockchip_spi *rs)
 
 static void rockchip_spi_set_cs(struct spi_device *spi, bool enable)
 {
-	u32 ser;
 	struct spi_master *master = spi->master;
 	struct rockchip_spi *rs = spi_master_get_devdata(master);
+	bool cs_asserted = !enable;
 
-	pm_runtime_get_sync(rs->dev);
+	/* Return immediately for no-op */
+	if (cs_asserted == rs->cs_asserted[spi->chip_select])
+		return;
 
-	ser = readl_relaxed(rs->regs + ROCKCHIP_SPI_SER) & SER_MASK;
+	if (cs_asserted) {
+		/* Keep things powered as long as CS is asserted */
+		pm_runtime_get_sync(rs->dev);
 
-	/*
-	 * drivers/spi/spi.c:
-	 * static void spi_set_cs(struct spi_device *spi, bool enable)
-	 * {
-	 *		if (spi->mode & SPI_CS_HIGH)
-	 *			enable = !enable;
-	 *
-	 *		if (spi->cs_gpio >= 0)
-	 *			gpio_set_value(spi->cs_gpio, !enable);
-	 *		else if (spi->master->set_cs)
-	 *		spi->master->set_cs(spi, !enable);
-	 * }
-	 *
-	 * Note: enable(rockchip_spi_set_cs) = !enable(spi_set_cs)
-	 */
-	if (!enable)
-		ser |= 1 << spi->chip_select;
-	else
-		ser &= ~(1 << spi->chip_select);
+		ROCKCHIP_SPI_SET_BITS(rs->regs + ROCKCHIP_SPI_SER,
+				      BIT(spi->chip_select));
+	} else {
+		ROCKCHIP_SPI_CLR_BITS(rs->regs + ROCKCHIP_SPI_SER,
+				      BIT(spi->chip_select));
 
-	writel_relaxed(ser, rs->regs + ROCKCHIP_SPI_SER);
+		/* Drop reference from when we first asserted CS */
+		pm_runtime_put(rs->dev);
+	}
 
-	pm_runtime_put_sync(rs->dev);
+	rs->cs_asserted[spi->chip_select] = cs_asserted;
 }
 
 static int rockchip_spi_prepare_message(struct spi_master *master,
@@ -739,7 +740,7 @@ static int rockchip_spi_probe(struct platform_device *pdev)
 	master->auto_runtime_pm = true;
 	master->bus_num = pdev->id;
 	master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_LOOP;
-	master->num_chipselect = 2;
+	master->num_chipselect = ROCKCHIP_SPI_MAX_CS_NUM;
 	master->dev.of_node = pdev->dev.of_node;
 	master->bits_per_word_mask = SPI_BPW_MASK(16) | SPI_BPW_MASK(8);
 
-- 
2.1.4