linux-kernel - [PATCH] serial: amba-pl011: do not request memory region twice

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Date:   Fri, 26 Nov 2021 15:39:25 +0100
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     gregkh@...uxfoundation.org
Cc:     linux@...linux.org.uk, jirislaby@...nel.org,
        p.rosenberger@...bus.com, lukas@...ner.de,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lino Sanfilippo <LinoSanfilippo@....de>
Subject: [PATCH] serial: amba-pl011: do not request memory region twice

The driver attempts to request and release the IO memory region for a uart
port twice:

First during the probe() function devm_ioremap_resource() is used to
allocate and map the ports memory.
Then a combo of pl011_config_port() and pl011_release_port() is used to
request/release the same memory area. These functions are called by the
serial core as soon as the uart is registered/unregistered.

However since the allocation request via devm_ioremap_resource() already
succeeds, the attempt to claim the memory again via pl011_config_port()
fails. This failure remains unnoticed, since the concerning return value is
not evaluated.
Later at module unload also the attempt to release the unclaimed memory
in pl011_release_port() fails. This time the failure results in a “Trying
to free nonexistent resource" warning printed by the serial core.

Fix these issues by removing the callbacks that implement the redundant
memory allocation/release.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@....de>
---

This patch was tested on a 5.10 Raspberry Pi kernel with a CM3.

 drivers/tty/serial/amba-pl011.c | 25 +------------------------
 1 file changed, 1 insertion(+), 24 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index d361cd84ff8c..91670ee25485 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2183,32 +2183,13 @@ static const char *pl011_type(struct uart_port *port)
 	return uap->port.type == PORT_AMBA ? uap->type : NULL;
 }

-/*
- * Release the memory region(s) being used by 'port'
- */
-static void pl011_release_port(struct uart_port *port)
-{
-	release_mem_region(port->mapbase, SZ_4K);
-}
-
-/*
- * Request the memory region(s) being used by 'port'
- */
-static int pl011_request_port(struct uart_port *port)
-{
-	return request_mem_region(port->mapbase, SZ_4K, "uart-pl011")
-			!= NULL ? 0 : -EBUSY;
-}
-
 /*
  * Configure/autoconfigure the port.
  */
 static void pl011_config_port(struct uart_port *port, int flags)
 {
-	if (flags & UART_CONFIG_TYPE) {
+	if (flags & UART_CONFIG_TYPE)
 		port->type = PORT_AMBA;
-		pl011_request_port(port);
-	}
 }

 /*
@@ -2275,8 +2256,6 @@ static const struct uart_ops amba_pl011_pops = {
 	.flush_buffer	= pl011_dma_flush_buffer,
 	.set_termios	= pl011_set_termios,
 	.type		= pl011_type,
-	.release_port	= pl011_release_port,
-	.request_port	= pl011_request_port,
 	.config_port	= pl011_config_port,
 	.verify_port	= pl011_verify_port,
 #ifdef CONFIG_CONSOLE_POLL
@@ -2306,8 +2285,6 @@ static const struct uart_ops sbsa_uart_pops = {
 	.shutdown	= sbsa_uart_shutdown,
 	.set_termios	= sbsa_uart_set_termios,
 	.type		= pl011_type,
-	.release_port	= pl011_release_port,
-	.request_port	= pl011_request_port,
 	.config_port	= pl011_config_port,
 	.verify_port	= pl011_verify_port,
 #ifdef CONFIG_CONSOLE_POLL

base-commit: a4849f6000e29235a2707f22e39da6b897bb9543
-- 
2.33.1