Re: [PATCH/RFC] pci: dynids.use_driver_data considered harmful

[Milton Miller]

On Aug 14, 2008, at 5:12 PM, Greg KH wrote:

> On Wed, Aug 06, 2008 at 09:31:18AM +0200, Jean Delvare wrote:
> > Hi Greg,
> >
> > On Thu, 17 Jul 2008 00:07:59 -0700, Greg KH wrote:
> > > On Wed, Jul 16, 2008 at 05:18:18AM -0500, Milton Miller wrote:
> > > > Greg,
> > > >
> > > > Please respond to this email and explain why the patch
> > > >
> > > > pci: dynids.use_driver_data considered harmful
> > > >
> > > > http://www.ussg.iu.edu/hypermail/linux/kernel/0807.1/index.html#2188
> > > >
> > > > should not be applied.   I am not arguing the correctness of
> > > > the removed code, rather its utility and benefit to the linux
> > > > community.
> > >
> > > (...)  I'll try to get
> > > to this by Monday, but my original point still stands, this was
> > > implemented for a reason,
> >
> > Not a good enough argument, sorry. There have been many cases in the
> > past where code has been withdrawn after some times because we
> > realized that we got it wrong in the first place.
>
> Fair enough :)
>
> > So, please explain what the current code is good for. Honestly, my
> > initial reaction to Milton's proposal was "what an idiot, this flag is
> > there for an obvious safety reason and we don't want to remove it" but
> > after reading both his arguments and the code, I found that I have
> > nothing to backup my claim. If you do, please let us know your
> > technical reasons.
>
> The technical reason was that this flag was needed to let some drivers
> work properly with the new_id file, right?
>
> If the flag goes away, they break from what I can tell.

That is not a detailed technical argument, its an  assumption.

> > >                           saying that not enough drivers use it 
> > > properly
> > > does not make the need for it to go away.  It is required for them, 
> > > so
> > > perhaps the other 419 drivers also need to have the flag set.  That's
> > > pretty trivial to do, right?
> >
> > If you are suggesting to blindly set the flag to all PCI drivers (or
> > even just all the ones which make use of the driver_data field -
> > doesn't make a difference), this simply shows how useless this flag 
> > is.
> > If you don't, then one would have to check the code of all drivers and
> > add validation code for the driver_data value; but then this no longer
> > falls into the "trivial" category.
>
> It's pretty "trivial" to look to see if the field is set in the pci_id
> structure, that should be all that is needed, right?


So please identify at least one such driver where the only correct 
answer is 0.  I even made it easy for you, i identified which drivers 
set dynamic_id and how.  I identified specific drivers where its the 
wrong answer.

So:  If you are arguing the code is still needed, please identify  at 
least one case that it is correct.  (Oh, I don't buy that if 0 is safe 
but 1 is equally safe, that the existing code is correct).

milton

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