linux-kernel - Re: PROBLEM: full speed HID device with payload of 64 bytes

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Date:	Thu, 13 Aug 2009 13:33:59 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	"Zeisel, Michael" <michael.zeisel@...lips.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-usb@...r.kernel.org
Subject: Re: PROBLEM: full speed HID device with payload of 64 bytes


[ added linux-usb to CC ]

On Thu, 13 Aug 2009, Zeisel, Michael wrote:

> We experienced those problems with one of our devices, the Digital 
> Pocket Memo 3 (DPM), by simply trying to receive button events via the
> 
> Cat /dev/usb/hiddev0
> 
> Command -> no success. The only difference between this device and older 
> ones (which work on this kernel version) in the USB descriptor is the 
> data payload which is 64 byte.
> 
> To narrow down the cause for that behavior we simply took the same 
> device, put in a FW with a low speed device protocol with a data payload 
> of 8 byte and plugged it again to the PC.
> 
> Now the button events produced some symbols in the "terminal", which 
> proves that the device was recognized correctly and works.
> 
> According to the USB 2.0 specification under
> 
> http://www.usb.org/developers/docs/
> 
> USB 2.0 specification, Chapter 5.7.4: Interrupt Transfer Bus Access Constraints
> 
> A full speed device should support a maximum data payload of 64 bytes 
> (Table 5-7. Full-speed Interrupt Transaction Limits: max.payload 64 
> bytes x max.transfers 19 = max. 1216bytes/frame)
> 
> To us it seems that the current implementation of the HID device support 
> in LINUX just supports the protocol for low speed devices (Table 5-6. 
> Low-speed Interrupt Transaction Limits: max.payload 8 bytes x 
> max.transfers 6 = max. 48bytes/frame)
> 
> On Windows OS and Mac OS all our devices work properly.

Could you please compile your kernel with CONFIG_USB_DEBUG and 
CONFIG_HID_DEBUG enabled, modprobe the 'hid' module with 'debug=2' 
parameter, and post the dmesg output that appears when you connect the 
device and press the buttons?

> I think it is a good idea, if you would have a Digital Pocket Memo to 
> experience the described behavior- so to whom I should send that device?

Let's see if something obvious pops out from the kernel debugging logs 
first.

Thanks,

-- 
Jiri Kosina
SUSE Labs

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