Patch "serial: 8250_lpss: Balance reference count for PCI DMA device" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    serial: 8250_lpss: Balance reference count for PCI DMA device

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     serial-8250_lpss-balance-reference-count-for-pci-dma.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 0976874be96f992dfa6482a180b0dfa1a5824eeb
Author: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Date:   Wed Feb 23 17:12:40 2022 +0200

    serial: 8250_lpss: Balance reference count for PCI DMA device
    
    [ Upstream commit 5318f70da7e82649d794fc27d8a127c22aa3566e ]
    
    The pci_get_slot() increases its reference count, the caller
    must decrement the reference count by calling pci_dev_put().
    
    Fixes: 9a1870ce812e ("serial: 8250: don't use slave_id of dma_slave_config")
    Depends-on: a13e19cf3dc1 ("serial: 8250_lpss: split LPSS driver to separate module")
    Reported-by: Qing Wang <wangqing@xxxxxxxx>
    Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20220223151240.70248-1-andriy.shevchenko@xxxxxxxxxxxxxxx
    Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/tty/serial/8250/8250_lpss.c b/drivers/tty/serial/8250/8250_lpss.c
index 848d81e3838c..49ae73f4d3a0 100644
--- a/drivers/tty/serial/8250/8250_lpss.c
+++ b/drivers/tty/serial/8250/8250_lpss.c
@@ -121,8 +121,7 @@ static int byt_serial_setup(struct lpss8250 *lpss, struct uart_port *port)
 {
 	struct dw_dma_slave *param = &lpss->dma_param;
 	struct pci_dev *pdev = to_pci_dev(port->dev);
-	unsigned int dma_devfn = PCI_DEVFN(PCI_SLOT(pdev->devfn), 0);
-	struct pci_dev *dma_dev = pci_get_slot(pdev->bus, dma_devfn);
+	struct pci_dev *dma_dev;
 
 	switch (pdev->device) {
 	case PCI_DEVICE_ID_INTEL_BYT_UART1:
@@ -141,6 +140,8 @@ static int byt_serial_setup(struct lpss8250 *lpss, struct uart_port *port)
 		return -EINVAL;
 	}
 
+	dma_dev = pci_get_slot(pdev->bus, PCI_DEVFN(PCI_SLOT(pdev->devfn), 0));
+
 	param->dma_dev = &dma_dev->dev;
 	param->m_master = 0;
 	param->p_master = 1;
@@ -156,6 +157,14 @@ static int byt_serial_setup(struct lpss8250 *lpss, struct uart_port *port)
 	return 0;
 }
 
+static void byt_serial_exit(struct lpss8250 *lpss)
+{
+	struct dw_dma_slave *param = &lpss->dma_param;
+
+	/* Paired with pci_get_slot() in the byt_serial_setup() above */
+	put_device(param->dma_dev);
+}
+
 static int ehl_serial_setup(struct lpss8250 *lpss, struct uart_port *port)
 {
 	struct uart_8250_dma *dma = &lpss->data.dma;
@@ -171,6 +180,13 @@ static int ehl_serial_setup(struct lpss8250 *lpss, struct uart_port *port)
 	return 0;
 }
 
+static void ehl_serial_exit(struct lpss8250 *lpss)
+{
+	struct uart_8250_port *up = serial8250_get_port(lpss->data.line);
+
+	up->dma = NULL;
+}
+
 #ifdef CONFIG_SERIAL_8250_DMA
 static const struct dw_dma_platform_data qrk_serial_dma_pdata = {
 	.nr_channels = 2,
@@ -345,8 +361,7 @@ static int lpss8250_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	return 0;
 
 err_exit:
-	if (lpss->board->exit)
-		lpss->board->exit(lpss);
+	lpss->board->exit(lpss);
 	pci_free_irq_vectors(pdev);
 	return ret;
 }
@@ -357,8 +372,7 @@ static void lpss8250_remove(struct pci_dev *pdev)
 
 	serial8250_unregister_port(lpss->data.line);
 
-	if (lpss->board->exit)
-		lpss->board->exit(lpss);
+	lpss->board->exit(lpss);
 	pci_free_irq_vectors(pdev);
 }
 
@@ -366,12 +380,14 @@ static const struct lpss8250_board byt_board = {
 	.freq = 100000000,
 	.base_baud = 2764800,
 	.setup = byt_serial_setup,
+	.exit = byt_serial_exit,
 };
 
 static const struct lpss8250_board ehl_board = {
 	.freq = 200000000,
 	.base_baud = 12500000,
 	.setup = ehl_serial_setup,
+	.exit = ehl_serial_exit,
 };
 
 static const struct lpss8250_board qrk_board = {