linux-kernel - Re: [LinuxBIOS] #57: libusb host program for PLX NET20DC debug device

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Message-ID: <m1wt5bfces.fsf@ebiederm.dsl.xmission.com>
Date:	Fri, 01 Dec 2006 16:02:03 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Peter Stuge <stuge-linuxbios@....org>
Cc:	Greg KH <gregkh@...e.de>, Andi Kleen <ak@...e.de>,
	Stefan Reinauer <stepan@...esystems.de>,
	linuxbios@...uxbios.org, linux-kernel@...r.kernel.org,
	"Lu, Yinghai" <yinghai.lu@....com>
Subject: Re: [LinuxBIOS] #57: libusb host program for PLX NET20DC debug device

Peter Stuge <stuge-linuxbios@....org> writes:

> On Fri, Dec 01, 2006 at 02:15:24PM -0700, Eric W. Biederman wrote:
>> Right.  For LinuxBIOS not a problem for earlyprintk in the kernel
>> somethings might need to be refactored.  The challenge in the
>> kernel is we don't know at build to how to do a pci_read_config...
>> 
>> The other hard part early in the kernel is the fact that the
>> bar is memory mapped I/O.  Which means it will need to get mapped
>> into the kernels page tables.
>
> I see.
>
>
>> >> And I have some code that barely works for this already, perhaps
>> >> Eric and I should work together on this :)
>> >
>> > I would be interested in having a look at any code for it too.
>> 
>> Sure, I will send it out shortly.  I currently have a working
>> user space libusb thing (easy, but useful for my debug)
>
> Hm - for driving which end?

Either.  The specific device we are talking about doesn't care.

>> and a rude read/write to the bar from user space program that
>
> How does that work? /dev/{port,mem}?

mmap /dev/mem.

>> allowed me to debug the worst of the state machine from user
>> space.  I don't think I have the state setup logic correct yet
>> but that is minor in comparison.
>> 
>> I really wish the EHCI spec had made that stupid interface 16 bytes
>> instead of 8 or had a way to chain multiple access together.  The
>> we could have used a normal usb cable.  As it is most descriptors
>> are 1 byte too big to read.
>
> Which descriptors are you reading?

Minor.  I was just wishing for less magic in this process, which
would make these kinds of devices much more available.

> The debug port isn't really supposed to be used with anything but a
> debug device - which can't be enumerated normally anyway.

It depends.  If you have a debug cable with magic ends and a hardcoded
address of 127 the normal enumeration doesn't work.  I don't think
anyone actually makes one of those.  Debug devices are also allowed to
be normal devices that just support the debug descriptor.  Which
is what I'm working with.

Eric

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