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From: Konrad Dybcio <konrad.dybcio@linaro.org>
Date: Thu, 01 Feb 2024 18:01:12 +0100
Subject: [PATCH] Revert "tty: serial: amba-pl011: Remove QDF2xxx
 workarounds"
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Message-Id: <20240201-topic-qdf24xx_is_back_apparently-v1-1-edb112a2ef90@linaro.org>
To: Russell King <linux@armlinux.org.uk>, 
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>, 
 Jiri Slaby <jirislaby@kernel.org>
Cc: Marijn Suijten <marijn.suijten@somainline.org>, 
 linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, 
 Marek Szyprowski <m.szyprowski@samsung.com>, 
 Mark Brown <broonie@kernel.org>, Konrad Dybcio <konrad.dybcio@linaro.org>

The original commit assumed this hardware is long rotting in the
junkyards, but apparently Qualcomm is still using some of these old
servers internally and the thing can still run upstream.

Adding insult to injury, I apparently managed to overdelete code and broke
non-QDF2xxx platforms [1].

Revert the removal to keep things going, at least for now.

This reverts commit 196f34af2bf4c87ac4299a9775503d81b446980c.

[1] https://lore.kernel.org/lkml/20240131213543.958051-1-m.szyprowski@samsung.com/

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
---
 drivers/tty/serial/amba-pl011.c | 82 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index c4df9cbc264b..fccec1698a54 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -152,6 +152,23 @@ static const struct vendor_data vendor_sbsa = {
 	.fixed_options		= true,
 };
 
+#ifdef CONFIG_ACPI_SPCR_TABLE
+static const struct vendor_data vendor_qdt_qdf2400_e44 = {
+	.reg_offset		= pl011_std_offsets,
+	.fr_busy		= UART011_FR_TXFE,
+	.fr_dsr			= UART01x_FR_DSR,
+	.fr_cts			= UART01x_FR_CTS,
+	.fr_ri			= UART011_FR_RI,
+	.inv_fr			= UART011_FR_TXFE,
+	.access_32b		= true,
+	.oversampling		= false,
+	.dma_threshold		= false,
+	.cts_event_workaround	= false,
+	.always_enabled		= true,
+	.fixed_options		= true,
+};
+#endif
+
 static u16 pl011_st_offsets[REG_ARRAY_SIZE] = {
 	[REG_DR] = UART01x_DR,
 	[REG_ST_DMAWM] = ST_UART011_DMAWM,
@@ -2451,6 +2468,15 @@ static int pl011_console_match(struct console *co, char *name, int idx,
 	resource_size_t addr;
 	int i;
 
+	/*
+	 * 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;
 
@@ -2491,6 +2517,22 @@ static struct console amba_console = {
 
 #define AMBA_CONSOLE	(&amba_console)
 
+static void qdf2400_e44_putc(struct uart_port *port, unsigned char c)
+{
+	while (readl(port->membase + UART01x_FR) & UART01x_FR_TXFF)
+		cpu_relax();
+	writel(c, port->membase + UART01x_DR);
+	while (!(readl(port->membase + UART01x_FR) & UART011_FR_TXFE))
+		cpu_relax();
+}
+
+static void qdf2400_e44_early_write(struct console *con, const char *s, unsigned int n)
+{
+	struct earlycon_device *dev = con->data;
+
+	uart_console_write(&dev->port, s, n, qdf2400_e44_putc);
+}
+
 static void pl011_putc(struct uart_port *port, unsigned char c)
 {
 	while (readl(port->membase + UART01x_FR) & UART01x_FR_TXFF)
@@ -2569,6 +2611,29 @@ OF_EARLYCON_DECLARE(pl011, "arm,pl011", pl011_early_console_setup);
 
 OF_EARLYCON_DECLARE(pl011, "arm,sbsa-uart", pl011_early_console_setup);
 
+/*
+ * On Qualcomm Datacenter Technologies QDF2400 SOCs affected by
+ * Erratum 44, traditional earlycon can be enabled by specifying
+ * "earlycon=qdf2400_e44,<address>".  Any options are ignored.
+ *
+ * Alternatively, you can just specify "earlycon", and the early console
+ * will be enabled with the information from the SPCR table.  In this
+ * case, the SPCR code will detect the need for the E44 work-around,
+ * and set the console name to "qdf2400_e44".
+ */
+static int __init
+qdf2400_e44_early_console_setup(struct earlycon_device *device,
+				const char *opt)
+{
+	if (!device->port.membase)
+		return -ENODEV;
+
+	device->con->write = qdf2400_e44_early_write;
+	return 0;
+}
+
+EARLYCON_DECLARE(qdf2400_e44, qdf2400_e44_early_console_setup);
+
 #else
 #define AMBA_CONSOLE	NULL
 #endif
@@ -2804,6 +2869,22 @@ static int pl011_resume(struct device *dev)
 
 static SIMPLE_DEV_PM_OPS(pl011_dev_pm_ops, pl011_suspend, pl011_resume);
 
+#ifdef CONFIG_ACPI_SPCR_TABLE
+static void qpdf2400_erratum44_workaround(struct device *dev,
+					  struct uart_amba_port *uap)
+{
+	if (!qdf2400_e44_present)
+		return;
+
+	dev_info(dev, "working around QDF2400 SoC erratum 44\n");
+	uap->vendor = &vendor_qdt_qdf2400_e44;
+}
+#else
+static void qpdf2400_erratum44_workaround(struct device *dev,
+					  struct uart_amba_port *uap)
+{ /* empty */ }
+#endif
+
 static int sbsa_uart_probe(struct platform_device *pdev)
 {
 	struct uart_amba_port *uap;
@@ -2840,6 +2921,7 @@ static int sbsa_uart_probe(struct platform_device *pdev)
 	uap->port.irq	= ret;
 
 	uap->vendor = &vendor_sbsa;
+	qpdf2400_erratum44_workaround(&pdev->dev, uap);
 
 	uap->reg_offset	= uap->vendor->reg_offset;
 	uap->fifosize	= 32;

---
base-commit: 51b70ff55ed88edd19b080a524063446bcc34b62
change-id: 20240201-topic-qdf24xx_is_back_apparently-146fc604e365

Best regards,
-- 
Konrad Dybcio <konrad.dybcio@linaro.org>