On Mon, 22 Sep 2014, Scot Doyle wrote:
> According to commit 0cce2eda19923e5e5ccc8b042dec5af87b3ffad0
> USB: fix LANGID=0 regression
>
> usb devices are not required to report string descriptors. Since they are
> optional, log an info message instead of an error message. In addition,
> use a higher level info message while moving the details to a debug message.
>
> Tested with USB device 0930:021c.
This is a good description, but it's not what the patch actually does.
> Signed-off-by: Scot Doyle <lkml14@xxxxxxxxxxxxx>
> ---
> drivers/usb/core/message.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
> index 0c8a7fc..6b95de7 100644
> --- a/drivers/usb/core/message.c
> +++ b/drivers/usb/core/message.c
> @@ -766,7 +766,7 @@ static int usb_get_langid(struct usb_device *dev, unsigned char *tbuf)
>
> /* If the string was reported but is malformed, default to english
> * (0x0409) */
> - if (err == -ENODATA || (err > 0 && err < 4)) {
> + if (err > 0 && err < 4) {
Why treat ENODATA as a separate case? It's just like the others -- the
device returned some data, but the data was malformed.
If the device really does not support string descriptors at all, err
would be equal to -EPIPE.
> dev->string_langid = 0x0409;
> dev->have_langid = 1;
> dev_err(&dev->dev,
> @@ -776,6 +776,18 @@ static int usb_get_langid(struct usb_device *dev, unsigned char *tbuf)
> return 0;
> }
>
> + /* If the string was unavailable, default to english (0x0409) */
-ENODATA doesn't mean the string was unavailable. It means that the
second byte of the reply was different from USB_DT_STRING, i.e., the
reply was malformed.
> + if (err == -ENODATA) {
> + dev->string_langid = 0x0409;
> + dev->have_langid = 1;
> + dev_info(&dev->dev,
> + "no string descriptor language, defaulting to English");
> + dev_dbg(&dev->dev,
> + "string descriptor 0 unavailable (err = -ENODATA), "
> + "defaulting to 0x%04x\n", dev->string_langid);
> + return 0;
> + }
Therefore this section is completely unnecessary.
> +
> /* In case of all other errors, we assume the device is not able to
> * deal with strings at all. Set string_langid to -1 in order to
> * prevent any string to be retrieved from the device */
And down here is where you should call either dev_info() or dev_err(),
depending on whether err is equal to -EPIPE or something else.
Alan Stern
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