linux-kernel - [PATCH] serial: 8250_bcm7271: Fix arbitration handling

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Message-Id: <20230309190224.687380-1-opendmb@gmail.com>
Date:   Thu,  9 Mar 2023 11:02:24 -0800
From:   Doug Berger <opendmb@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Al Cooper <alcooperx@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Doug Berger <opendmb@...il.com>
Subject: [PATCH] serial: 8250_bcm7271: Fix arbitration handling

The arbitration of the UART DMA is mishandled for a few
exceptional cases when probing and releasing the driver.

It is possible that the DMA register spaces are not defined in
device tree for an instance of the driver, so attempts to access
the registers in brcmuart_arbitration() would use NULL pointers.

It is also possible for the probe function to return an error
while still holding the UART DMA. This would prevent the UART
DMA from being claimed by an instance that could use it.

These errors are addressed by only releasing the UART DMA if it
is held by this instance (i.e. priv->dma_enabled == 1) and
directing early error paths in probe to this common release_dma
handling.

Fixes: 41a469482de2 ("serial: 8250: Add new 8250-core based Broadcom STB driver")
Signed-off-by: Doug Berger <opendmb@...il.com>
---
 drivers/tty/serial/8250/8250_bcm7271.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_bcm7271.c b/drivers/tty/serial/8250/8250_bcm7271.c
index ed5a94747692..f801b1f5b46c 100644
--- a/drivers/tty/serial/8250/8250_bcm7271.c
+++ b/drivers/tty/serial/8250/8250_bcm7271.c
@@ -1014,14 +1014,16 @@ static int brcmuart_probe(struct platform_device *pdev)
 	/* See if a Baud clock has been specified */
 	baud_mux_clk = of_clk_get_by_name(np, "sw_baud");
 	if (IS_ERR(baud_mux_clk)) {
-		if (PTR_ERR(baud_mux_clk) == -EPROBE_DEFER)
-			return -EPROBE_DEFER;
+		if (PTR_ERR(baud_mux_clk) == -EPROBE_DEFER) {
+			ret = -EPROBE_DEFER;
+			goto release_dma;
+		}
 		dev_dbg(dev, "BAUD MUX clock not specified\n");
 	} else {
 		dev_dbg(dev, "BAUD MUX clock found\n");
 		ret = clk_prepare_enable(baud_mux_clk);
 		if (ret)
-			return ret;
+			goto release_dma;
 		priv->baud_mux_clk = baud_mux_clk;
 		init_real_clk_rates(dev, priv);
 		clk_rate = priv->default_mux_rate;
@@ -1029,7 +1031,8 @@ static int brcmuart_probe(struct platform_device *pdev)
 
 	if (clk_rate == 0) {
 		dev_err(dev, "clock-frequency or clk not defined\n");
-		return -EINVAL;
+		ret = -EINVAL;
+		goto release_dma;
 	}
 
 	dev_dbg(dev, "DMA is %senabled\n", priv->dma_enabled ? "" : "not ");
@@ -1116,7 +1119,9 @@ static int brcmuart_probe(struct platform_device *pdev)
 	serial8250_unregister_port(priv->line);
 err:
 	brcmuart_free_bufs(dev, priv);
-	brcmuart_arbitration(priv, 0);
+release_dma:
+	if (priv->dma_enabled)
+		brcmuart_arbitration(priv, 0);
 	return ret;
 }
 
@@ -1128,7 +1133,8 @@ static int brcmuart_remove(struct platform_device *pdev)
 	hrtimer_cancel(&priv->hrt);
 	serial8250_unregister_port(priv->line);
 	brcmuart_free_bufs(&pdev->dev, priv);
-	brcmuart_arbitration(priv, 0);
+	if (priv->dma_enabled)
+		brcmuart_arbitration(priv, 0);
 	return 0;
 }
 
-- 
2.34.1