FAILED: patch "[PATCH] serial: qcom-geni: fix polled console corruption" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x 63d14d974d3d82d0feeae8c73b055d330051e1b4
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024100159-chatty-uncombed-a25a@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

63d14d974d3d ("serial: qcom-geni: fix polled console corruption")
cc4a0e5754a1 ("serial: qcom-geni: fix console corruption")
f97cdbbf187f ("serial: qcom-geni: fix false console tx restart")
947cc4ecc06c ("serial: qcom-geni: fix soft lockup on sw flow control and suspend") 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo")
f8fef2fa419f ("tty: msm_serial: use dmaengine_prep_slave_sg()")
9054605ab846 ("tty: 8250_omap: use dmaengine_prep_slave_sg()")
8192fabb0db2 ("tty: 8250_dma: use dmaengine_prep_slave_sg()")
3bcb0bf65c2b ("Merge tag 'tty-6.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 63d14d974d3d82d0feeae8c73b055d330051e1b4 Mon Sep 17 00:00:00 2001
From: Johan Hovold <[email protected]>
Date: Fri, 6 Sep 2024 15:13:36 +0200
Subject: [PATCH] serial: qcom-geni: fix polled console corruption
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The polled UART operations are used by the kernel debugger (KDB, KGDB), which can interrupt the kernel at any point in time. The current Qualcomm GENI implementation does not really work when there is on-going serial output as it inadvertently "hijacks" the current tx command, which can result in both the initial debugger output being corrupted as well as the corruption of any on-going serial output (up to 4k characters) when execution resumes:

0190: abcdefghijklmnopqrstuvwxyz0123456789 0190: abcdefghijklmnopqrstuvwxyz0123456789
0191: abcdefghijklmnop[ 50.825552] sysrq: DEBUG
qrstuvwxyz0123456789 0191: abcdefghijklmnopqrstuvwxyz0123456789
Entering kdb (current=0xffff53510b4cd280, pid 640) on processor 2 due to Keyboard Entry [2]kdb> go
omlji3h3h2g2g1f1f0e0ezdzdycycxbxbwawav :t72r2rp o9n976k5j5j4i4i3h3h2g2g1f1f0e0ezdzdycycxbxbwawavu:t7t8s8s8r2r2q0q0p o9n9n8ml6k6k5j5j4i4i3h3h2g2g1f1f0e0ezdzdycycxbxbwawav v u:u:t9t0s4s4rq0p
o9n9n8m8m7l7l6k6k5j5j40q0p p o
o9n9n8m8m7l7l6k6k5j5j4i4i3h3h2g2g1f1f0e0ezdzdycycxbxbwawav :t8t9s4s4r4r4q0q0p

Fix this by making sure that the polled output implementation waits for the tx fifo to drain before cancelling any on-going longer transfers. As the polled code cannot take any locks, leave the state variables as they are and instead make sure that the interrupt handler always starts a new tx command when there is data in the write buffer.

Since the debugger can interrupt the interrupt handler when it is writing data to the tx fifo, it is currently not possible to fully prevent losing up to 64 bytes of tty output on resume.

index f23fd0ac3cfd..6f0db310cf69 100644
@@ -145,6 +145,7 @@ static const struct uart_ops qcom_geni_uart_pops;
 static struct uart_driver qcom_geni_console_driver;
 static struct uart_driver qcom_geni_uart_driver;
 
+static void __qcom_geni_serial_cancel_tx_cmd(struct uart_port *uport);
 static void qcom_geni_serial_cancel_tx_cmd(struct uart_port *uport);
 
 static inline struct qcom_geni_serial_port *to_dev_port(struct uart_port *uport)

@@ -384,13 +385,14 @@ static int qcom_geni_serial_get_char(struct uart_port *uport)
 static void qcom_geni_serial_poll_put_char(struct uart_port *uport,
 							unsigned char c)
 {
-	writel(DEF_TX_WM, uport->membase + SE_GENI_TX_WATERMARK_REG);
+	if (qcom_geni_serial_main_active(uport)) {
+		qcom_geni_serial_poll_tx_done(uport);
+		__qcom_geni_serial_cancel_tx_cmd(uport);
+	}
+
 	writel(M_CMD_DONE_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
 	qcom_geni_serial_setup_tx(uport, 1);
-	WARN_ON(!qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
-						M_TX_FIFO_WATERMARK_EN, true));
 	writel(c, uport->membase + SE_GENI_TX_FIFOn);
-	writel(M_TX_FIFO_WATERMARK_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
 	qcom_geni_serial_poll_tx_done(uport);
 }
 #endif

@@ -677,13 +679,10 @@ static void qcom_geni_serial_stop_tx_fifo(struct uart_port *uport)
 	writel(irq_en, uport->membase + SE_GENI_M_IRQ_EN);
 }
 
-static void qcom_geni_serial_cancel_tx_cmd(struct uart_port *uport)
+static void __qcom_geni_serial_cancel_tx_cmd(struct uart_port *uport)
 {
 	struct qcom_geni_serial_port *port = to_dev_port(uport);
 
-	if (!qcom_geni_serial_main_active(uport))
-		return;
-
 	geni_se_cancel_m_cmd(&port->se);
 	if (!qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
 						M_CMD_CANCEL_EN, true)) {

@@ -693,6 +692,16 @@ static void qcom_geni_serial_cancel_tx_cmd(struct uart_port *uport)
 		writel(M_CMD_ABORT_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
 	}
 	writel(M_CMD_CANCEL_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
+}
+
+static void qcom_geni_serial_cancel_tx_cmd(struct uart_port *uport)
+{
+	struct qcom_geni_serial_port *port = to_dev_port(uport);
+
+	if (!qcom_geni_serial_main_active(uport))
+		return;
+
+	__qcom_geni_serial_cancel_tx_cmd(uport);
 
 	port->tx_remaining = 0;
 	port->tx_queued = 0;

@@ -919,7 +928,7 @@ static void qcom_geni_serial_handle_tx_fifo(struct uart_port *uport,
 	if (!chunk)
 		goto out_write_wakeup;
 
-	if (!port->tx_remaining) {
+	if (!active) {
 		qcom_geni_serial_setup_tx(uport, pending);
 		port->tx_remaining = pending;
 		port->tx_queued = 0;