[PATCH] disable RTS override on LPSS UART with Auto Flow Control

[Dan O'Donovan]

Currently, Auto Flow Control is not working correctly on the Atom
X5-Z8350 "Cherry Trail" SoC, because an "RTS override" feature is
enabled in a vendor-specific register in the LPSS UART. The symptom
is that RTS is not de-asserted as it should be when RTS/CTS flow
control is enabled and the RX FIFO fills up.

This appears to be introduced by commit 1f47a77c4e49 ("ACPI / LPSS:
not using UART RTS override with Auto Flow Control").

To _disable_ the RTS override, bit 3 needs to be _set_ in the
"GENERAL" register at offset 808h.  The power-on default is 0. The
aforementioned commit appears to have assumed the inverse of this.

Signed-off-by: Dan O'Donovan <d...@emutex.com>
---
 drivers/acpi/acpi_lpss.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/acpi_lpss.c b/drivers/acpi/acpi_lpss.c
index 8ea836c..4b3f2d5 100644
--- a/drivers/acpi/acpi_lpss.c
+++ b/drivers/acpi/acpi_lpss.c
@@ -45,7 +45,7 @@ ACPI_MODULE_NAME("acpi_lpss");
 #define LPSS_RESETS_RESET_APB          BIT(1)
 #define LPSS_GENERAL                   0x08
 #define LPSS_GENERAL_LTR_MODE_SW       BIT(2)
-#define LPSS_GENERAL_UART_RTS_OVRD     BIT(3)
+#define LPSS_GENERAL_UART_RTS_NO_OVRD  BIT(3)
 #define LPSS_SW_LTR                    0x10
 #define LPSS_AUTO_LTR                  0x14
 #define LPSS_LTR_SNOOP_REQ             BIT(15)
@@ -123,10 +123,10 @@ static void lpss_uart_setup(struct lpss_private_data 
*pdata)
        writel(val | LPSS_TX_INT_MASK, pdata->mmio_base + offset);
 
        val = readl(pdata->mmio_base + LPSS_UART_CPR);
-       if (!(val & LPSS_UART_CPR_AFCE)) {
+       if (val & LPSS_UART_CPR_AFCE) {
                offset = pdata->dev_desc->prv_offset + LPSS_GENERAL;
                val = readl(pdata->mmio_base + offset);
-               val |= LPSS_GENERAL_UART_RTS_OVRD;
+               val |= LPSS_GENERAL_UART_RTS_NO_OVRD;
                writel(val, pdata->mmio_base + offset);
        }
 }
-- 
2.7.4