USB: gadget: f_printer: set a default q_len

The usb_f_printer gadget driver uses a default q_len value of *0* which prevents
any IO from occurring.  Moreover, once the driver is instantiated it is
impossible to change the q_len value.

The following patch uses a default q_len value of 10 which matches the legacy
g_printer gadget driver.  This minimizes the possibility that you end up with a
non-working printer gadget.  It is still possible to set the q_len to a
different value using the configfs path of the same name.

Signed-off-by: Michael R Sweet <msweet@msweet.org>
Link: https://lore.kernel.org/r/9DFB1605-63A5-46DB-A5A4-B59B315D8115@msweet.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
index 64a4112..31eba2a 100644 (file)
--- a/drivers/usb/gadget/function/f_printer.c
+++ b/drivers/usb/gadget/function/f_printer.c
@@ -51,6 +51,8 @@
 #define GET_PORT_STATUS                1
 #define SOFT_RESET             2
 
+#define DEFAULT_Q_LEN          10 /* same as legacy g_printer gadget */
+
 static int major, minors;
 static struct class *usb_gadget_class;
 static DEFINE_IDA(printer_ida);
@@ -1363,6 +1365,9 @@ static struct usb_function_instance *gprinter_alloc_inst(void)
        opts->func_inst.free_func_inst = gprinter_free_inst;
        ret = &opts->func_inst;
 
+       /* Make sure q_len is initialized, otherwise the bound device can't support read/write! */
+       opts->q_len = DEFAULT_Q_LEN;
+
        mutex_lock(&printer_ida_lock);
 
        if (ida_is_empty(&printer_ida)) {