[PATCH] [for 4.13] tty: pl011: fix initialization order of QDF2400 E44

[Timur Tabi <timur@codeaurora.org>]

The work-around for Qualcomm Technologies QDF2400 Erratum 44 hinges on a
global variable defined in the pl011 driver.  The ACPI SPCR parsing code
determines whether the work-around is needed, and if so, it changes the
console name from "pl011" to "qdf2400_e44".  The expectation is that
the pl011 driver will implement the work-around when it sees the console
name.  The global variable qdf2400_e44_present is set when that happens.

The problem is that work-around needs to be enabled when the pl011
driver probes, not when the console name is queried.  However, sbsa_probe()
is called before pl011_console_match().  The work-around appeared to work
previously because the default console on QDF2400 platforms was always
ttyAMA1.  The first time sbsa_probe() is called (for ttyAMA0),
qdf2400_e44_present is still false.  Then pl011_console_match() is called,
and it sets qdf2400_e44_present to true.  All subsequent calls to
sbsa_probe() enable the work-around.

The solution is to move the global variable into spcr.c and let the
pl011 driver query it during probe time.  This works because all QDF2400
platforms require SPCR, so parse_spcr() will always be called.
pl011_console_match still checks for the "qdf2400_e44" console name,
but it doesn't do anything else special.

Fixes: 5a0722b898f8 ("tty: pl011: use "qdf2400_e44" as the earlycon name for QDF2400 E44")
Tested-by: Jeffrey Hugo <jhugo@codeaurora.org>
Signed-off-by: Timur Tabi <timur@codeaurora.org>
---
 drivers/acpi/spcr.c             | 36 ++++++++++++++++++++++++++++++++++--
 drivers/tty/serial/amba-pl011.c | 37 +++++++++++++++++++------------------
 include/linux/acpi.h            |  1 +
 3 files changed, 54 insertions(+), 20 deletions(-)

diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
index 4ac3e06b41d8..98aa8c808a33 100644
--- a/drivers/acpi/spcr.c
+++ b/drivers/acpi/spcr.c
@@ -17,6 +17,16 @@
 #include <linux/serial_core.h>
 
 /*
+ * Erratum 44 for QDF2432v1 and QDF2400v1 SoCs describes the BUSY bit as
+ * occasionally getting stuck as 1. To avoid the potential for a hang, check
+ * TXFE == 0 instead of BUSY == 1. This may not be suitable for all UART
+ * implementations, so only do so if an affected platform is detected in
+ * parse_spcr().
+ */
+bool qdf2400_e44_present;
+EXPORT_SYMBOL(qdf2400_e44_present);
+
+/*
  * Some Qualcomm Datacenter Technologies SoCs have a defective UART BUSY bit.
  * Detect them by examining the OEM fields in the SPCR header, similiar to PCI
  * quirk detection in pci_mcfg.c.
@@ -147,8 +157,30 @@ int __init parse_spcr(bool earlycon)
 		goto done;
 	}
 
-	if (qdf2400_erratum_44_present(&table->header))
-		uart = "qdf2400_e44";
+	/*
+	 * If the E44 erratum is required, then we need to tell the pl011
+	 * driver to implement the work-around.
+	 *
+	 * The global variable is used by the probe function when it
+	 * creates the UARTs, whether or not they're used as a console.
+	 *
+	 * If the user specifies "traditional" earlycon, the qdf2400_e44
+	 * console name matches the EARLYCON_DECLARE() statement, and
+	 * SPCR is not used.  Parameter "earlycon" is false.
+	 *
+	 * If the user specifies "SPCR" earlycon, then we need to update
+	 * the console name so that it also says "qdf2400_e44".  Parameter
+	 * "earlycon" is true.
+	 *
+	 * For consistency, if we change the console name, then we do it
+	 * for everyone, not just earlycon.
+	 */
+	if (qdf2400_erratum_44_present(&table->header)) {
+		qdf2400_e44_present = true;
+		if (earlycon)
+			uart = "qdf2400_e44";
+	}
+
 	if (xgene_8250_erratum_present(table))
 		iotype = "mmio32";
 
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 8a857bb34fbb..1888d168a41c 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -142,15 +142,7 @@ static unsigned int get_fifosize_arm(struct amba_device *dev)
 	.fixed_options		= true,
 };
 
-/*
- * Erratum 44 for QDF2432v1 and QDF2400v1 SoCs describes the BUSY bit as
- * occasionally getting stuck as 1. To avoid the potential for a hang, check
- * TXFE == 0 instead of BUSY == 1. This may not be suitable for all UART
- * implementations, so only do so if an affected platform is detected in
- * parse_spcr().
- */
-static bool qdf2400_e44_present = false;
-
+#ifdef CONFIG_ACPI_SPCR_TABLE
 static struct vendor_data vendor_qdt_qdf2400_e44 = {
 	.reg_offset		= pl011_std_offsets,
 	.fr_busy		= UART011_FR_TXFE,
@@ -165,6 +157,7 @@ static unsigned int get_fifosize_arm(struct amba_device *dev)
 	.always_enabled		= true,
 	.fixed_options		= true,
 };
+#endif
 
 static u16 pl011_st_offsets[REG_ARRAY_SIZE] = {
 	[REG_DR] = UART01x_DR,
@@ -2375,12 +2368,14 @@ static int __init pl011_console_match(struct console *co, char *name, int idx,
 	resource_size_t addr;
 	int i;
 
-	if (strcmp(name, "qdf2400_e44") == 0) {
-		pr_info_once("UART: Working around QDF2400 SoC erratum 44");
-		qdf2400_e44_present = true;
-	} else if (strcmp(name, "pl011") != 0) {
+	/*
+	 * Systems affected by the Qualcomm Technologies QDF2400 E44 erratum
+	 * have a distinct console name, so make sure we check for that.
+	 * The actual implementation of the erratum occurs in the probe
+	 * function.
+	 */
+	if ((strcmp(name, "qdf2400_e44") != 0) && (strcmp(name, "pl011") != 0))
 		return -ENODEV;
-	}
 
 	if (uart_parse_earlycon(options, &iotype, &addr, &options))
 		return -ENODEV;
@@ -2734,11 +2729,17 @@ static int sbsa_uart_probe(struct platform_device *pdev)
 	}
 	uap->port.irq	= ret;
 
-	uap->reg_offset	= vendor_sbsa.reg_offset;
-	uap->vendor	= qdf2400_e44_present ?
-					&vendor_qdt_qdf2400_e44 : &vendor_sbsa;
+#ifdef CONFIG_ACPI_SPCR_TABLE
+	if (qdf2400_e44_present) {
+		dev_info(&pdev->dev, "working around QDF2400 SoC erratum 44\n");
+		uap->vendor = &vendor_qdt_qdf2400_e44;
+	} else
+#endif
+		uap->vendor = &vendor_sbsa;
+
+	uap->reg_offset	= uap->vendor->reg_offset;
 	uap->fifosize	= 32;
-	uap->port.iotype = vendor_sbsa.access_32b ? UPIO_MEM32 : UPIO_MEM;
+	uap->port.iotype = uap->vendor->access_32b ? UPIO_MEM32 : UPIO_MEM;
 	uap->port.ops	= &sbsa_uart_pops;
 	uap->fixed_baud = baudrate;
 
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index c749eef1daa1..27b4b6615263 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -1209,6 +1209,7 @@ static inline void acpi_table_upgrade(void) { }
 #endif
 
 #ifdef CONFIG_ACPI_SPCR_TABLE
+extern bool qdf2400_e44_present;
 int parse_spcr(bool earlycon);
 #else
 static inline int parse_spcr(bool earlycon) { return 0; }
-- 
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm
Technologies, Inc.  Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.