[PATCH 07/12] drm/amdgpu: implement cgs gpu memory callbacks

[Christian König]

On 30.09.2015 08:54, Daniel Vetter wrote:
> On Tue, Sep 29, 2015 at 04:28:13PM -0400, Alex Deucher wrote:
>> On Tue, Sep 29, 2015 at 4:10 PM, Dave Airlie <airlied at gmail.com> wrote:
>>> On 30 September 2015 at 01:41, Alex Deucher <alexdeucher at gmail.com> wrote:
>>>> On Tue, Sep 29, 2015 at 11:20 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
>>>>> On Tue, Sep 29, 2015 at 02:39:49PM +0200, Christian König wrote:
>>>>>> On 29.09.2015 13:40, Daniel Vetter wrote:
>>>>>>> On Thu, Jul 09, 2015 at 12:21:06PM -0400, Alex Deucher wrote:
>>>>>>>> From: Chunming Zhou <david1.zhou at amd.com>
>>>>>>>>
>>>>>>>> This implements the cgs interface for allocating
>>>>>>>> GPU memory.
>>>>>>>>
>>>>>>>> Reviewed-by: Jammy Zhou <Jammy.Zhou at amd.com>
>>>>>>> I don't see that review anywhere on a m-l ... where is it?
>>>>>> Jammy reviewed the stuff internally before we made it public, that's why you
>>>>>> can't find it.
>>> Can we get these reviews done publically? it's kinda hard to know how
>>> well someone
>>> reviewed things if we have no external copy. Like did Jammy a) read
>>> the patch, and
>>> slap Reviewed-by on it, or did he b) comment on some whitespace issues
>>> and slap R-b
>>> on it, or c) did he suggest a bunch of changes and those changes were
>>> made and a new
>>> version was produced and he r-b'ed that etc.
>>>
>> We are pushing for that and making steady progress, but things are
>> slow to move internally.
>>
>>>>> The other stuff seems a lot more benign. For the irq abstraction
>>>>> specifically it might be worth looking at the irq_chip stuff linux core
>>>>> has, which is what's used to virtualize/abstract irq routing and handling.
>>>>> But for that stuff it's a balance thing really how much you reinvent
>>>>> wheels internally in the driver (e.g. i915 has it's own power_well stuff
>>>>> which is pretty much just powerdomains reinvented, with less features).
>>>>>
>>>> I think that's one of the hardest things in the kernel: finding out if
>>>> a solution already exists or not.  We implemented our own version of
>>>> mfd for our ACP audio block driver.  Upon upsteaming we were alerted
>>>> to mfd's existence and we converted the driver to use mfd.  At the end
>>>> of the day it was a lot of work for minimal gain, at least from a
>>>> functionality perspective.  I wish we had known about it sooner.  I'll
>>>> take a look at the irq_chip stuff.  Thanks for the heads up!
>>> You say for minimal gain, but this is pretty much going to keep happening
>>> to you with the development model you have chosen, get used to rewriting
>>> things you consider finished and reviewed. I've said it before so I'll use this
>>> to reiterate, your patches are only starting the process when you post them,
>>> all the internal stuff you do is nice and all but it could all be done
>>> externally
>>> if you guys weren't so stuck on internal IP review. Otherwise you
>>> should be taking
>>> into account that this overhead will continue to exist in all your development,
>>> and adjust schedules to suit.
>> We do take that into account as evidenced by the multiple revisions of
>> the ACP patch set for example.  We know there may be a delta between
>> short term deliverables and what eventually goes upstream and we take
>> that into account.  That doesn't change the overall amount of work
>> involved.  The fact is we didn't know about mfd so we didn't use it.
>> I don't see how we could have avoided rewriting it if we didn't know
>> about it in the first place.  When we sent the patches out, we found
>> out about it and made the appropriate changes.  My point was just that
>> we aren't the only ones this happens to.
> Discussing early designs on irc helps a lot with that. But ime irc is one
> step further away from just dragging engineers onto the mailing list, and
> discussing new stuff on irc before patches get written instead of just
> review is one step more. That still leaves you with the problem with
> knowing whom to talk to, but for modularization we have at least Thierry
> Reding and Laurent Pinchart with a lot of soc experience outside of drm,
> they tend to know what's out there.

Yeah, completely agree.

Alex and I have spend a lot of time and effort with developers 
previously working on closed source code to enable them to contribute to 
the different open source projects.

Anybody who did something like that before knows that it certainly needs 
time for certain concepts to sink in. Especially thinks like stable 
interface and certain design criteria seem to be hard to get accepted.

So guys feel to criticize the code whenever you think it make sense and 
please do so as early as possible, e.g. on the first round of patches 
not after ten revisions.

We in turn try to get the code out as soon as possible, without keeping 
it stuck internally for too long.

Christian.

> -Daniel