[PATCH v2 tty-next] 8250: microchip: pci1xxxx: Add PCIe Hot reset disable support for Rev C0 and later devices

[Rengarajan S <rengarajan.s@microchip.com>]

Systems that issue PCIe hot reset requests during a suspend/resume
cycle cause PCI1XXXX device revisions prior to C0 to get its UART
configuration registers reset to hardware default values. This results
in device inaccessibility and data transfer failures. Starting with
Revision C0, support was added in the device hardware (via the Hot
Reset Disable Bit) to allow resetting only the PCIe interface and its
associated logic, but preserving the UART configuration during a hot
reset. This patch enables the hot reset disable feature during suspend/
resume for C0 and later revisions of the device.

v2
Retained the original writel and simplified the hot reset condition
v1
Initial Commit.

Signed-off-by: Rengarajan S <rengarajan.s@microchip.com>
---
 drivers/tty/serial/8250/8250_pci1xxxx.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_pci1xxxx.c b/drivers/tty/serial/8250/8250_pci1xxxx.c
index e9c51d4e447d..61849312393b 100644
--- a/drivers/tty/serial/8250/8250_pci1xxxx.c
+++ b/drivers/tty/serial/8250/8250_pci1xxxx.c
@@ -115,6 +115,7 @@
 
 #define UART_RESET_REG				0x94
 #define UART_RESET_D3_RESET_DISABLE		BIT(16)
+#define UART_RESET_HOT_RESET_DISABLE            BIT(17)
 
 #define UART_BURST_STATUS_REG			0x9C
 #define UART_TX_BURST_FIFO			0xA0
@@ -620,6 +621,10 @@ static int pci1xxxx_suspend(struct device *dev)
 	}
 
 	data = readl(p + UART_RESET_REG);
+
+	if (priv->dev_rev >= 0xC0)
+		data |= UART_RESET_HOT_RESET_DISABLE;
+
 	writel(data | UART_RESET_D3_RESET_DISABLE, p + UART_RESET_REG);
 
 	if (wakeup)
@@ -647,7 +652,12 @@ static int pci1xxxx_resume(struct device *dev)
 	}
 
 	data = readl(p + UART_RESET_REG);
+
+	if (priv->dev_rev >= 0xC0)
+		data &= ~UART_RESET_HOT_RESET_DISABLE;
+
 	writel(data & ~UART_RESET_D3_RESET_DISABLE, p + UART_RESET_REG);
+
 	iounmap(p);
 
 	for (i = 0; i < priv->nr; i++) {
-- 
2.25.1