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

[Milton Miller <miltonm@bga.com>]

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 past where code has been withdrawn after some times because we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