From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg KH <greg@kroah.com>,
Mauro Carvalho Chehab <mchehab@redhat.com>,
Stephen Rothwell <sfr@canb.auug.org.au>,
linux-next@vger.kernel.org, linux-kernel@vger.kernel.org,
Alan Cox <alan@linux.intel.com>,
"Igor M. Liplianin" <liplianin@me.by>,
Ben Gamari <bgamari.foss@gmail.com>
Subject: Re: Kernelspace firmware loaders (was: linux-next: manual merge of the staging tree with the v4l-dvb tree)
Date: Wed, 9 Mar 2011 23:30:59 +0100 [thread overview]
Message-ID: <201103092331.00774.laurent.pinchart@ideasonboard.com> (raw)
In-Reply-To: <AANLkTi=Yavz4=KYNgsR02yTmBU_+BigC9qCSdX4SrTF2@mail.gmail.com>
Hi Linus,
On Monday 07 March 2011 17:39:43 Linus Torvalds wrote:
> On Mon, Mar 7, 2011 at 8:16 AM, Greg KH <greg@kroah.com> wrote:
> > If the code is just a "pass-through" to the hardware, I have no
> > objection to the driver being in the kernel, if it needs to be in order
> > to control the hardware properly.
>
> .. or even if it doesn't "need to be", and you _could_ do it in user space.
>
> We've had tons of problems with user space breakage and version skew
> etc. It's often been a total pain to have user space-vs-kernel
> components that support one version but not the other, making it hard
> to upgrade the kernel independently of other things. The whole
> experience with X-vs-drm has been very painful.
>
> There are two cases where user-space drivers work fine:
>
> (a) if there is no kernel component to them at all. Think "this
> driver would work on not just Linux, but on FreeBSD and UnixWare".
> Examples of this would be the original X approach.
>
> (b) if there's a kernel driver which exports an interface that is
> specified by the hardware (NOT specified by some "abstraction" layer),
> and where the kernel just exports an interface and doesn't expect
> anything back (ie the kernel is _strictly_ the lower-level driver,
> there is no two-way "user space helps kernel" crap)
>
> A reasonable example of this would be the USB user space drivers:
> the kernel interface is clearly _below_ (so the kernel does not depend
> on user space), and the defined not by some crazy software interface,
> but by the USB hardware standard.
>
> But any other kind of mixing is just a big pain. Having a user-space
> thing to set things up for a kernel driver is crazy crap. It
> inevitably leads to "one or the other is broken, and people working on
> one piece aren't the same people working on the other". Just don't do
> it. Every time it's done, it leads to problems. You need special
> programs to set things up etc. It's just f*cked up.
>
> (An example of why it's crazy crap: it inevitably means that the
> kernel can not "resume" a device. Because it now needs user space help
> to get the device going again. Crazy. Don't do it. It's shit).
I agree with you on the pain introduced by mixing drivers with userspace
helpers. However, I'm still concerned about having a full JTAG stack in the
kernel.
The Altera JTAG driver is basically a firmware loader. There's nothing wrong
with firmare loaders in the kernel per-se, we have plenty of them and they
usually request firmware data from userspace (hopefully specially crafted for
the Linux driver, or pre-processed when the firmware is extracted from a
Windows driver) and more of less dump it to the device.
Now, if a vendor provided a firmware in the form of a Java bytecode file,
requiring the kernel driver to implement a JVM to load the firmware into the
device, would you accept it ? JTAG is not Java, but it still requires several
non-trivial layers, from controller drivers (we need to support multiple APIs
there, as controllers can range from simple bit-banging adapters to more
complex and faster devices with a higher level interface) to binary firmware
interpreters (and I'm really talking about intepreters here, not just parsers
- the Altera firmware file requires a VM) with of course incompatible vendor-
specific formats.
--
Regards,
Laurent Pinchart
next prev parent reply other threads:[~2011-03-09 22:30 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-04 5:39 linux-next: manual merge of the staging tree with the v4l-dvb tree Stephen Rothwell
2011-03-04 17:13 ` Greg KH
2011-03-04 17:54 ` Mauro Carvalho Chehab
2011-03-04 21:23 ` Greg KH
2011-03-04 22:17 ` Mauro Carvalho Chehab
2011-03-07 14:07 ` Kernelspace firmware loaders (was: linux-next: manual merge of the staging tree with the v4l-dvb tree) Laurent Pinchart
2011-03-07 16:16 ` Greg KH
2011-03-07 16:39 ` Linus Torvalds
2011-03-09 22:30 ` Laurent Pinchart [this message]
2011-03-10 8:14 ` Olivier Galibert
2011-03-07 16:51 ` Laurent Pinchart
2011-03-07 17:40 ` Igor M. Liplianin
2011-03-09 22:11 ` Laurent Pinchart
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