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From:   Vincent MAILHOL <mailhol.vincent@wanadoo.fr>
Date:   Sun, 13 Nov 2022 00:40:31 +0900
Message-ID: <CAMZ6Rq+N7Dbs7AENU12PJu-M2coBeoEF-YLpvQp79cSChAR6hg@mail.gmail.com>
Subject: Re: [PATCH v2 3/3] can: etas_es58x: report the firmware version
 through ethtool
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Alan Stern <stern@rowland.harvard.edu>, linux-can@vger.kernel.org,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org
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On Mon. 7 nov. 2022 at 01:18, Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
> On Sun, Nov 06, 2022 at 11:44:52PM +0900, Vincent MAILHOL wrote:
> > On Sun. 6 Nov. 2022 à 23:22, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> > > On Sun, Nov 06, 2022 at 09:47:05PM +0900, Vincent MAILHOL wrote:
> > > > On Sun. 6 Nov. 2022 at 20:25, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> > > > 1/ Can I still export and use usb_cache_string()? In other terms, does
> > > > the first patch of this series still apply? This looks like the most
> > > > convenient function to retrieve that custom string to me.
> > >
> > > Everyone seems to just use the usb_string() function, will that not work
> > > for you?
> >
> > It is just that I would have to write two or three lines of code less.
>
> Odd, should it be used instead where others are calling usb_string()?
>
> > But if you prefer I can use usb_string(), no problem on that.
>
> Try it both ways.  If it's easier with usb_cache_string(), then we can
> export it.  It's just odd that it hasn't been exported yet.

I tried both. Not counting the line breaks, the empty lines and the
comments, the usb_string() version needs 6 more lines. Not a huge
difference but the usb_cache_string() remains easier (at least in my
eyes).

For reference, here is the diff before and after using usb_cache_string():

diff --git a/drivers/net/can/usb/etas_es58x/es58x_sysfs.c
b/drivers/net/can/usb/etas_es58x/es58x_sysfs.c
index 4ff0332f6f50..c1d220d0d35f 100644
--- a/drivers/net/can/usb/etas_es58x/es58x_sysfs.c
+++ b/drivers/net/can/usb/etas_es58x/es58x_sysfs.c
@@ -178,17 +178,10 @@ void es58x_create_file(struct device *dev)
 {
        struct es58x_device *es58x_dev = dev_get_drvdata(dev);
        char *prod_info;
-       int ret;

-       prod_info = kmalloc(ES58X_PROD_INFO_SIZE, GFP_KERNEL);
-       if (!prod_info)
-               return;
-
-        ret = usb_string(es58x_dev->udev, ES58X_PROD_INFO_IDX,
-                        prod_info, ES58X_PROD_INFO_SIZE);
-        if (ret < 0) {
+       prod_info = usb_cache_string(es58x_dev->udev, ES58X_PROD_INFO_IDX);
+       if (!prod_info) {
                dev_warn(dev, "could not retrieve the product info string\n");
-               kfree(prod_info);
                return;
        }

diff --git a/drivers/net/can/usb/etas_es58x/es58x_sysfs.h
b/drivers/net/can/usb/etas_es58x/es58x_sysfs.h
index 62347ffa0214..a204aa5344a8 100644
--- a/drivers/net/can/usb/etas_es58x/es58x_sysfs.h
+++ b/drivers/net/can/usb/etas_es58x/es58x_sysfs.h
@@ -14,13 +14,6 @@
 /* USB descriptor index containing the product information string. */
 #define ES58X_PROD_INFO_IDX 6

-/* Maximum size for the USB information custom string. USB strings are
- * at most 127 characters and es58x devices only use ASCII (i.e. one
- * byte). Also, empirical observations show a maximum length of 83
- * bytes for the product information.
- */
-#define ES58X_PROD_INFO_SIZE (127 + 1)
-
 void es58x_create_file(struct device *dev);
 void es58x_remove_file(struct device *dev);