usb: max-3421: Use driver data instead of maintaining a list of bound devices

Instead of maintaining a single-linked list of devices that must be
searched linearly in .remove() just use spi_set_drvdata() to remember the
link between the spi device and the driver struct. Then the global list
and the next member can be dropped.

This simplifies the driver, reduces the memory footprint and the time to
search the list. Also it makes obvious that there is always a corresponding
driver struct for a given device in .remove(), so the error path for
!max3421_hcd can be dropped, too.

As a side effect this fixes a data inconsistency when .probe() races with
itself for a second max3421 device in manipulating max3421_hcd_list. A
similar race is fixed in .remove(), too.

Fixes: 2d53139f31 ("Add support for using a MAX3421E chip as a host driver.")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20211018204028.2914597-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/max3421-hcd.c

@@ -125,8 +125,6 @@ struct max3421_hcd {
 
 	struct task_struct *spi_thread;
 
-	struct max3421_hcd *next;
-
 	enum max3421_rh_state rh_state;
 	/* lower 16 bits contain port status, upper 16 bits the change mask: */
 	u32 port_status;
@@ -174,8 +172,6 @@ struct max3421_ep {
 	u8 retransmit;			/* packet needs retransmission */
 };
 
-static struct max3421_hcd *max3421_hcd_list;
-
 #define MAX3421_FIFO_SIZE	64
 
 #define MAX3421_SPI_DIR_RD	0	/* read register from MAX3421 */
@@ -1882,9 +1878,8 @@ max3421_probe(struct spi_device *spi)
 	}
 	set_bit(HCD_FLAG_POLL_RH, &hcd->flags);
 	max3421_hcd = hcd_to_max3421(hcd);
-	max3421_hcd->next = max3421_hcd_list;
-	max3421_hcd_list = max3421_hcd;
 	INIT_LIST_HEAD(&max3421_hcd->ep_list);
+	spi_set_drvdata(spi, max3421_hcd);
 
 	max3421_hcd->tx = kmalloc(sizeof(*max3421_hcd->tx), GFP_KERNEL);
 	if (!max3421_hcd->tx)
@@ -1934,28 +1929,18 @@ error:
 static int
 max3421_remove(struct spi_device *spi)
 {
-	struct max3421_hcd *max3421_hcd = NULL, **prev;
-	struct usb_hcd *hcd = NULL;
+	struct max3421_hcd *max3421_hcd;
+	struct usb_hcd *hcd;
 	unsigned long flags;
 
-	for (prev = &max3421_hcd_list; *prev; prev = &(*prev)->next) {
-		max3421_hcd = *prev;
-		hcd = max3421_to_hcd(max3421_hcd);
-		if (hcd->self.controller == &spi->dev)
-			break;
-	}
-	if (!max3421_hcd) {
-		dev_err(&spi->dev, "no MAX3421 HCD found for SPI device %p\n",
-			spi);
-		return -ENODEV;
-	}
+	max3421_hcd = spi_get_drvdata(spi);
+	hcd = max3421_to_hcd(max3421_hcd);
 
 	usb_remove_hcd(hcd);
 
 	spin_lock_irqsave(&max3421_hcd->lock, flags);
 
 	kthread_stop(max3421_hcd->spi_thread);
-	*prev = max3421_hcd->next;
 
 	spin_unlock_irqrestore(&max3421_hcd->lock, flags);