[PATCH AUTOSEL 4.14 05/15] spi: pxa2xx: Add CS control clock quirk

[Sasha Levin <sashal@xxxxxxxxxx>]

From: Evan Green <evgreen@xxxxxxxxxxxx>

[ Upstream commit 683f65ded66a9a7ff01ed7280804d2132ebfdf7e ]

In some circumstances on Intel LPSS controllers, toggling the LPSS
CS control register doesn't actually cause the CS line to toggle.
This seems to be failure of dynamic clock gating that occurs after
going through a suspend/resume transition, where the controller
is sent through a reset transition. This ruins SPI transactions
that either rely on delay_usecs, or toggle the CS line without
sending data.

Whenever CS is toggled, momentarily set the clock gating register
to "Force On" to poke the controller into acting on CS.

Signed-off-by: Rajat Jain <rajatja@xxxxxxxxxx>
Signed-off-by: Evan Green <evgreen@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200211223700.110252-1-rajatja@xxxxxxxxxx
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/spi/spi-pxa2xx.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/spi/spi-pxa2xx.c b/drivers/spi/spi-pxa2xx.c
index b2245cdce230b..5160e16d3a985 100644
--- a/drivers/spi/spi-pxa2xx.c
+++ b/drivers/spi/spi-pxa2xx.c
@@ -76,6 +76,10 @@ MODULE_ALIAS("platform:pxa2xx-spi");
 #define LPSS_CAPS_CS_EN_SHIFT			9
 #define LPSS_CAPS_CS_EN_MASK			(0xf << LPSS_CAPS_CS_EN_SHIFT)
 
+#define LPSS_PRIV_CLOCK_GATE 0x38
+#define LPSS_PRIV_CLOCK_GATE_CLK_CTL_MASK 0x3
+#define LPSS_PRIV_CLOCK_GATE_CLK_CTL_FORCE_ON 0x3
+
 struct lpss_config {
 	/* LPSS offset from drv_data->ioaddr */
 	unsigned offset;
@@ -92,6 +96,8 @@ struct lpss_config {
 	unsigned cs_sel_shift;
 	unsigned cs_sel_mask;
 	unsigned cs_num;
+	/* Quirks */
+	unsigned cs_clk_stays_gated : 1;
 };
 
 /* Keep these sorted with enum pxa_ssp_type */
@@ -162,6 +168,7 @@ static const struct lpss_config lpss_platforms[] = {
 		.tx_threshold_hi = 56,
 		.cs_sel_shift = 8,
 		.cs_sel_mask = 3 << 8,
+		.cs_clk_stays_gated = true,
 	},
 };
 
@@ -385,6 +392,22 @@ static void lpss_ssp_cs_control(struct driver_data *drv_data, bool enable)
 	else
 		value |= LPSS_CS_CONTROL_CS_HIGH;
 	__lpss_ssp_write_priv(drv_data, config->reg_cs_ctrl, value);
+	if (config->cs_clk_stays_gated) {
+		u32 clkgate;
+
+		/*
+		 * Changing CS alone when dynamic clock gating is on won't
+		 * actually flip CS at that time. This ruins SPI transfers
+		 * that specify delays, or have no data. Toggle the clock mode
+		 * to force on briefly to poke the CS pin to move.
+		 */
+		clkgate = __lpss_ssp_read_priv(drv_data, LPSS_PRIV_CLOCK_GATE);
+		value = (clkgate & ~LPSS_PRIV_CLOCK_GATE_CLK_CTL_MASK) |
+			LPSS_PRIV_CLOCK_GATE_CLK_CTL_FORCE_ON;
+
+		__lpss_ssp_write_priv(drv_data, LPSS_PRIV_CLOCK_GATE, value);
+		__lpss_ssp_write_priv(drv_data, LPSS_PRIV_CLOCK_GATE, clkgate);
+	}
 }
 
 static void cs_assert(struct driver_data *drv_data)
-- 
2.20.1