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Date: Tue, 28 Jul 2009 13:31:23 -0600
From: Robert Hancock <hancockrwd@gmail.com>
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To: Daniel J Blueman <daniel.blueman@gmail.com>
CC: Linux Kernel <linux-kernel@vger.kernel.org>,
       Linux USB <linux-usb-devel@lists.sourceforge.net>
Subject: Re: [2.6.31-rc4] ftdi_usb maps memory from stack...
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On 07/27/2009 04:17 PM, Daniel J Blueman wrote:
> With DMA debugging enabled, I see a warning when the FTDI USB-serial
> driver loads [1] using a non-DMAable address.
>
> I can get a disassembly of some of the stack frames to identify the
> exact call-sites etc, if that helps anyone?
>
> Thanks,
>    Daniel
>
> --- [1]
>
> usbcore: registered new interface driver usbserial_generic
>
> usbserial: USB Serial Driver core
>
> USB Serial support registered for FTDI USB Serial Device
>
> ftdi_sio 5-1:1.0: FTDI USB Serial Device converter detected
>
> usb 5-1: Detected FT8U232AM
>
> usb 5-1: Number of endpoints 2
>
> usb 5-1: Endpoint 1 MaxPacketSize 64
>
> usb 5-1: Endpoint 2 MaxPacketSize 64
>
> usb 5-1: Setting MaxPacketSize 64
>
> ------------[ cut here ]------------
>
> WARNING: at lib/dma-debug.c:856 check_for_stack+0x9a/0xc0()
>
> Hardware name: OEM
>
> uhci_hcd 0000:00:1d.0: DMA-API: device driver maps memory from stack
> [addr=ffff88007f89b946]

Looks like some of the functions in ftdi_sio.c call usb_control_msg with 
a stack buffer and some use a kmalloc buffer. They should likely all be 
using a kmalloc buffer.