[linux-dvb] [PATCH 1/7] Adding empia base driver

Hans Verkuil hverkuil at xs4all.nl
Sat Nov 1 17:21:45 CET 2008


Hi Devin,

Just a few quick notes:

On Saturday 01 November 2008 16:46:03 Devin Heitmueller wrote:
> Hello,
>
> I have held off on offering an opinion this to see what others
> thought, but I think now may be the time to speak up.
>
> First off, a disclaimer: I am a contributor to the existing in-kernel
> em28xx driver.  I have spent many months working on that codebase,
> adding device support and fixing bugs.  I also have a large series of
> patches queuing up that significantly improve both the codebase's
> functionality and maintainability (having recently been given access
> to some of the datasheets thanks to Empia and Pinnacle).
>
> As one of the half dozen people who are working on the linux-dvb
> version of em28xx, I am against the wholesale replacement of the
> current version with Markus's codebase.

At this time I do not advocate replacing the current em28xx driver. But 
when they are both in the kernel, then I expect and hope that the best 
features of the em28xx driver are merged into the empia driver and that 
the current em28xx driver can eventually be dropped.

> Why?  I've got a list of reasons, but in the interest of fairness,
> let's start with what I see to be the good things:
>
> # Significantly better device support - Markus has access to the
> actual hardware for many of these devices, spends time adding support
> for new devices, and since he works for the chipset vendor can in
> many cases just call the manufacturer of the product and ask them
> questions.
>
> # Proper tuner locking - tuner locking was one of the big issues that
> caused infighting before Markus forked off his code. Let's face it -
> it's been over a year and most of the other devices don't do any
> locking at all. His scheme, while not unified across drivers, is
> better than nothing.
>
> # Based on the chipset datasheets - He had the benefit of just being
> able to look up what the registers mean
>
> # VBI support for analog - a recent addition in the mrec driver, but
> none at all in the V4L driver
>
> # Support for other demods not currently in V4L - I don't think we
> have any devices yet that use the LGDT3304, but Markus's driver has
> support for devices that do.
>
> # More thoroughly debugged - He's working on this full time. He's
> working bugs, dealing with issues, and putting in proper fixes based
> on reliable information instead of reverse engineering.
>
> ========
>
> Now, the not so good things:
>
> # Doesn't leverage common infrastructure such as videobuf (resulting
> in duplicate functionality and more difficult for those who have to
> maintain multiple drivers)

Definitely a candidate to merge into Markus' driver eventually. There 
are more drivers that do not use videobuf (my own ivtv and cx18 drivers 
spring to mind).

> # Firmware blobs embedded in source - While it's easier for the user,
> many distributions do not allow firmware blobs in the kernel due to
> the belief that this is not GPL compatible. We would need to get
> permission from the vendor to redistribute the firmware as a file (in
> the V4L driver, we extract it from the Windows driver binary)

From what I saw firmware blobs were only present in the xceive drivers, 
and it is my opinion that it is not a good idea to merge these into the 
kernel. Much better to fix the existing drivers. Having the empia 
driver into the kernel will actually force those fixes to be made.

> # Ambigious licensing - some of the files have headers from companies
> other than Empiatech which are very clearly not GPL compatible (like
> the Micronas drx3973d driver). Also, it's not clear that even the
> firmware blobs mentioned above are authorized to be redistributed by
> their rightful owners (Xceive and Micronas). While Empiatech may be
> ok with making a GPL driver, these parties have not consented to
> having their intellectual property in the kernel (they may have
> consented but the header files say just the opposite).

Licensing should obviously be addressed. But such drivers (except for 
the xceive ones) are currently not used by the empia sources as 
submitted by Markus.

> # It has its own xc3028 and xc5000 tuner driver. I don't know whether
> his driver is better than the one in V4L. Presumably he has the
> datasheets for those parts, but on the other hand the V4L driver
> allows loading of the firmware externally. The V4L drivers are also
> used by devices beyond the em28xx and may have functionality required
> by other companies products.

For the record: other devs have datasheets and sources as well for these 
devices.

> # What I'll call "Black magic" - lots of arbitrary code without any
> explanation as to what it is doing or why. Why does the DVB init
> routine write 0x77 to register 0x12? What does that do? A combination
> of poor use of constants and commented code combined with a lack of
> access to the datasheets leaves this a mystery. You just have to
> "trust that it's doing the right thing because it works"

This is not an uncommon occurence when datasheets are not public. 
Hopefully Markus can address such problems when the driver is in the 
kernel. It's IMHO not a blocking issue.

> # He's the only one who has access to the datasheets, so there is
> limited opportunity for peer review. The community driver is based on
> reverse engineering, and we can pass around USB traces we collect to
> justify/explain design decisions. How do you question a design when
> the basis of answers is essentially "because the secret document that
> I can't show you says so"?

There are lots of drivers that are based on NDAs (e.g. my cx18 driver). 
The code is public, but the datasheets aren't. That's actually much 
better than to rely on reverse engineering. Of course, you get the best 
results if the datasheets are also public, but that's sadly not always 
possible. Often active developers can all get NDAs, so that multiple 
devs have access to datasheets (again, that's the case for the cx18 
driver).

I see this as an advantage, not a disadvantage.

>
> ====
>
> I shared this list with Markus a few months ago and, the licensing
> issues aside, it was his contention that "nobody cares" about most of
> the things above.  As a maintainer that wants to continue
> contributing to the codebase, *I* care.  And I'm sure that anybody
> other than Markus who wants to understand the em28xx codebase and be
> able to fix bugs would also care.  I'm also concerned with
> consistency between drivers.  Having one driver do things differently
> than all the others is just a maintenance headache for those who have
> to support multiple drivers.
>
> A number of people have suggested that nobody was willing to
> incorporate Markus's changes incrementally to improve the in-kernel
> driver.  This couldn't be further from the truth.  I appealed to
> Markus on multiple occasions trying to find some compromise where his
> changes could be merged into the mainline em28xx driver.  He outright
> refused.  It was his contention that his driver was/is better than
> the in-kernel driver in every possible way, and that the existing
> code has no redeeming value.  In fact, I was accused of taking his
> GPL'd code without his consent and incorporating it into the
> linux-dvb codebase. It's this "all or nothing" attitude that has
> prevented his work thus far from being incorporated, not the
> unwillingness of people like myself to do the work to merge his
> changes in a sane matter.
>
> I *really* want to see this resolved, because I recognize that I
> could be better served working on other things than duplicating
> efforts to debug issues that Markus may have already fixed in his
> codebase.  But just throwing away the work of half a dozen other
> developers on an actively maintained driver is not really the sort of
> compromise I think would be best for the community.
>
> I'm sorry if the sharing of my views on this matter create more
> animosity within the community, as that is the exact opposite of what
> I want.

This is I think the last chance to get Markus' driver into the kernel. 
If this fails again, then there is no other choice but to fork it all. 
But for the end-users it's so much better if Markus would maintain the 
empia driver since he has the datasheets and hardware.

Forget the history, and see this as a new driver. I think I presented a 
reasonable roadmap for it to be merged.

Regards,

	Hans



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