linux-kernel - [PATCH v2 2/3] can: etas_es58x: use usb_cache_string() to retrieve the product info string

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Message-Id: <20221104171604.24052-3-mailhol.vincent@wanadoo.fr>
Date:   Sat,  5 Nov 2022 02:16:03 +0900
From:   Vincent Mailhol <mailhol.vincent@...adoo.fr>
To:     linux-can@...r.kernel.org
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>
Subject: [PATCH v2 2/3] can: etas_es58x: use usb_cache_string() to retrieve the product info string

Instead of allocating memory ourselves and doing all the error
handling, rely on usb_cache_string(). This results in simpler code.

Make es58x_get_product_info() return void. The reason is double:

  1/ by using usb_cache_string() we do not know anymore the root cause
     (is it an allocation issue or input/output issue?)

  2/ Failling to get the product info is not critical. So it is OK to
     continue.

Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
---
 drivers/net/can/usb/etas_es58x/es58x_core.c | 33 +++------------------
 drivers/net/can/usb/etas_es58x/es58x_core.h |  3 ++
 2 files changed, 7 insertions(+), 29 deletions(-)

diff --git a/drivers/net/can/usb/etas_es58x/es58x_core.c b/drivers/net/can/usb/etas_es58x/es58x_core.c
index 51294b717040..1a17aadfc1dc 100644
--- a/drivers/net/can/usb/etas_es58x/es58x_core.c
+++ b/drivers/net/can/usb/etas_es58x/es58x_core.c
@@ -2124,41 +2124,18 @@ static void es58x_free_netdevs(struct es58x_device *es58x_dev)
  * @es58x_dev: ES58X device.
  *
  * Do a synchronous call to get the product information.
- *
- * Return: zero on success, errno when any error occurs.
  */
-static int es58x_get_product_info(struct es58x_device *es58x_dev)
+static void es58x_get_product_info(struct es58x_device *es58x_dev)
 {
-	struct usb_device *udev = es58x_dev->udev;
-	const int es58x_prod_info_idx = 6;
-	/* Empirical tests show a prod_info length of maximum 83,
-	 * below should be more than enough.
-	 */
-	const size_t prod_info_len = 127;
 	char *prod_info;
-	int ret;
 
-	prod_info = kmalloc(prod_info_len, GFP_KERNEL);
+	prod_info = usb_cache_string(es58x_dev->udev, ES58X_PROD_INFO_IDX);
 	if (!prod_info)
-		return -ENOMEM;
+		return;
 
-	ret = usb_string(udev, es58x_prod_info_idx, prod_info, prod_info_len);
-	if (ret < 0) {
-		dev_err(es58x_dev->dev,
-			"%s: Could not read the product info: %pe\n",
-			__func__, ERR_PTR(ret));
-		goto out_free;
-	}
-	if (ret >= prod_info_len - 1) {
-		dev_warn(es58x_dev->dev,
-			 "%s: Buffer is too small, result might be truncated\n",
-			 __func__);
-	}
 	dev_info(es58x_dev->dev, "Product info: %s\n", prod_info);
 
- out_free:
 	kfree(prod_info);
-	return ret < 0 ? ret : 0;
 }
 
 /**
@@ -2243,9 +2220,7 @@ static int es58x_probe(struct usb_interface *intf,
 	if (IS_ERR(es58x_dev))
 		return PTR_ERR(es58x_dev);
 
-	ret = es58x_get_product_info(es58x_dev);
-	if (ret)
-		return ret;
+	es58x_get_product_info(es58x_dev);
 
 	for (ch_idx = 0; ch_idx < es58x_dev->num_can_ch; ch_idx++) {
 		ret = es58x_init_netdev(es58x_dev, ch_idx);
diff --git a/drivers/net/can/usb/etas_es58x/es58x_core.h b/drivers/net/can/usb/etas_es58x/es58x_core.h
index 640fe0a1df63..9a5a616df783 100644
--- a/drivers/net/can/usb/etas_es58x/es58x_core.h
+++ b/drivers/net/can/usb/etas_es58x/es58x_core.h
@@ -49,6 +49,9 @@
 /* A magic number sent by the ES581.4 to inform it is alive. */
 #define ES58X_HEARTBEAT 0x11
 
+/* USB descriptor index containing the product information string. */
+#define ES58X_PROD_INFO_IDX 6
+
 /**
  * enum es58x_driver_info - Quirks of the device.
  * @ES58X_DUAL_CHANNEL: Device has two CAN channels. If this flag is
-- 
2.37.4