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From:   Peter Chen <peter.chen@nxp.com>
To:     Michael R Sweet <msweet@msweet.org>
CC:     Felipe Balbi <balbi@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Fix default q_len for usb_f_printer gadget driver
Thread-Topic: [PATCH] Fix default q_len for usb_f_printer gadget driver
Thread-Index: AQHWrwzV9jtaofMn3Uubju/AT/ynNamwyWQA
Date:   Fri, 30 Oct 2020 23:24:29 +0000
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On 20-10-30 18:34:19, Michael R Sweet wrote:
> The usb_f_printer gadget driver uses a default q_len value of *0* which p=
revents
> any IO from occurring.  Moreover, once the driver is instantiated it is
> impossible to change the q_len value.
>=20
> The following patch uses a default q_len value of 10 which matches the le=
gacy
> 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.
>=20
> Signed-off-by: Michael R Sweet <msweet@msweet.org>

Reviewed-by: Peter Chen <peter.chen@nxp.com>

Peter
> ---
>  drivers/usb/gadget/function/f_printer.c | 5 +++++
>  1 file changed, 5 insertions(+)
>=20
> diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget=
/function/f_printer.c
> index 9c7ed2539ff7..4f3161005e4f 100644
> --- a/drivers/usb/gadget/function/f_printer.c
> +++ b/drivers/usb/gadget/function/f_printer.c
> @@ -50,6 +50,8 @@
>  #define GET_PORT_STATUS		1
>  #define SOFT_RESET		2
> =20
> +#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);
> @@ -1317,6 +1319,9 @@ static struct usb_function_instance *gprinter_alloc=
_inst(void)
>  	opts->func_inst.free_func_inst =3D gprinter_free_inst;
>  	ret =3D &opts->func_inst;
> =20
> +	/* Make sure q_len is initialized, otherwise the bound device can't sup=
port read/write! */
> +	opts->q_len =3D DEFAULT_Q_LEN;
> +
>  	mutex_lock(&printer_ida_lock);
> =20
>  	if (ida_is_empty(&printer_ida)) {
> --=20
> 2.17.1
>=20

--=20

Thanks,
Peter Chen=