linux-kernel - Re: Resend Re: [PATCH v6] usb:serial:pl2303: add GPIOs interface on PL2303

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Date:	Thu, 28 Aug 2014 07:38:10 +0800
From:	Wang YanQing <udknight@...il.com>
To:	Johan Hovold <johan@...nel.org>
Cc:	gregkh@...uxfoundation.org, linus.walleij@...aro.org,
	jhovold@...il.com, andi@...as.de, dforsi@...il.com,
	gnomes@...rguk.ukuu.org.uk, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Resend Re: [PATCH v6] usb:serial:pl2303: add GPIOs interface on
 PL2303

On Tue, Aug 12, 2014 at 04:02:59PM +0200, Johan Hovold wrote:
> On Sat, Aug 09, 2014 at 02:46:56AM +0800, Wang YanQing wrote:
> > On Fri, Aug 08, 2014 at 09:54:42AM +0200, Johan Hovold wrote:
> > > On Fri, Aug 08, 2014 at 03:10:34AM +0800, Wang YanQing wrote:
> > > > On Tue, Aug 05, 2014 at 03:54:08PM +0200, Johan Hovold wrote:
> > > > > > > I noticed that setting direction to output and setting the gpio high has
> > > > > > > no effect on the read-back value (i.e. I still read back 0) for my
> > > > > > > pl2303hx (note that my device has no easily accessible gpios so I
> > > > > > > haven't verified the actual state of the output pin).
> > > > > > > 
> > > > > > > What happens on your system? Is the read-back value still 0, even when
> > > > > > > the GPIO output is actually high? Should we return the cached value in
> > > > > > > this case?
> > > > > > 
> > > > > > If i set direction to output, then I could control gpio high and low
> > > > > > by set 1 or 0, and the read-back value is 1 or 0 according to high and
> > > > > > low(I test high and low by oscillscope)
> > > > > > 
> > > > > > I test it with my pl2303hx with only two gpios.
> > > > > >
> > > > > > Could you use usbmon to see whether the traffic is right according
> > > > > > to comment in struct pl2303_gpio?
> > > > > 
> > > > > The traffic appears correct judging from the debug output (which I
> > > > > trust). Output-enable is reflected in register 0x81, but the value
> > > > > isn't.
> > > > > 
> > > > > What is the lsusb -v output for your device?
> > > > 
> > > > Bus 001 Device 005: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port.
> > > 
> > > You forgot the verbose flag (-v).
> > Sorry, below is output with -v:
> > Bus 002 Device 004: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port
> > Device Descriptor:
> >   bLength                18
> >   bDescriptorType         1
> >   bcdUSB               1.10
> >   bDeviceClass            0 (Defined at Interface level)
> >   bDeviceSubClass         0 
> >   bDeviceProtocol         0 
> >   bMaxPacketSize0        64
> >   idVendor           0x067b Prolific Technology, Inc.
> >   idProduct          0x2303 PL2303 Serial Port
> >   bcdDevice            3.00
> 
> You seem to have an HX device, whereas mine is an HXD (rev D) with
> bcdDevice 4.00. That could account for the different behaviour of the
> GPIO state/value register.
> 
> How did you figure out which registers to use? Were you sniffing the
> traffic of some driver for some other OS? And does your device only have
> two GPIOs and not four like the HX rev D?

After I found I need to use GPIOs in pl2303, I found below patch in Internet firstly:
http://comments.gmane.org/gmane.linux.usb.general/65066

Then I verified the protocol by sniffing the traffic of some driver for some other
OS running in virtualbox, and host OS is linux:)

Prolific has pl2303 gpio test program (.exe) for windows, maybe you could find it
from Internet. It support HXA and HXD, I use it to test two gpios in my pl2303HXA, 
and analyze output of usbmon.

Yes, my device only have two GPIOs.
> <snip>
> 
> > > > It is strange your device doesn't work, I verify the control method by
> > > > analyze usbmon output from linux host which has VirtualBox running 
> > > > gpio test program, but I don't have right to distribute the gpio test
> > > > program I think, so I can't help you to figure out why it doesn't work 
> > > > for your device.
> > > 
> > > What do you use the gpio test program for? I thought you verified the
> > > gpios with a scope?
> > 
> > Yes, I verified gpios with a scope.
> > 
> > "
> > You must allocate the buffer dynamically as some platforms cannot do
> > DMA to the stack.
> > "
> > Thanks very much for point out it, could you clarify it? 
> > I want to know the reason.
> 
> The memory where the stack resides might not be available for DMA, and
> even if it is, there could still be problems with cache coherency.

It is still vague:
stack memory maybe resident higher place than normal memory,
but I don't think kmalloc could be immune from this problem, unless
we use GFP_DMA?
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