On Fri, 14 Oct 2011, Fabian Godehardt wrote:
> From: Christian Kellermann <ck@xxxxxxxxx>
>
> bMaxPacketSize specifies the maximum packet size for this endpoint in
> bytes. According to usb spec valid values are 8, 16, 32, 64.
>
> Without the patch the g_printer driver will fail the USB consortium's
> Chapter 9 conformity test suite. A value from the set above needs to
> be set.
Not true. Did you try it?
> For the printer device choosing the maximum value has been choosen to
> reduce overhead for data transfers.
>
> Signed-off-by: Christian Kellermann <ck@xxxxxxxxx>
> Signed-off-by: Fabian Godehardt <fg@xxxxxxxxx>
> ---
> drivers/usb/gadget/printer.c | 1 +
> 1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/usb/gadget/printer.c b/drivers/usb/gadget/printer.c
> index a341dde..9f6be75 100644
> --- a/drivers/usb/gadget/printer.c
> +++ b/drivers/usb/gadget/printer.c
> @@ -234,6 +234,7 @@ static struct usb_device_descriptor device_desc = {
> .iManufacturer = STRING_MANUFACTURER,
> .iProduct = STRING_PRODUCT,
> .iSerialNumber = STRING_SERIALNUM,
> + .bMaxPacketSize0 = 0x40,
> .bNumConfigurations = 1
> };
This patch is completely unnecessary (and wrong). Evidently you didn't
read the code that uses the device descriptor, in printer_setup():
case USB_DT_DEVICE:
device_desc.bMaxPacketSize0 =
gadget->ep0->maxpacket;
value = min(wLength, (u16) sizeof device_desc);
memcpy(req->buf, &device_desc, value);
break;
The bMaxPacketSize0 value is determined by the UDC driver, not the
gadget driver.
Alan Stern
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