Re: [Intel-gfx] [RFC PATCH v3 1/1] i915/drm: Split out x86/arm64 for run_as_guest

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 22/03/2022 15:26, Jani Nikula wrote:
> On Tue, 22 Mar 2022, Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> wrote:
>> On 22/03/2022 14:49, Jani Nikula wrote:
>>> On Tue, 22 Mar 2022, Lucas De Marchi <lucas.demarchi@intel.com> wrote:
>>>> On Tue, Mar 22, 2022 at 12:21:59PM +0200, Jani Nikula wrote:
>>>>> On Mon, 21 Mar 2022, Lucas De Marchi <lucas.demarchi@intel.com> wrote:
>>>>>> On Mon, Mar 21, 2022 at 04:34:49PM -0700, Casey Bowman wrote:
>>>>>>> Wanted to ping this older thread to find out where we stand with this patch,
>>>>>>> Are we OK with the current state of these changes?
>>>>>>>
>>>>>>> With more recent information gathered from feedback on other patches, would
>>>>>>> we prefer changing this to a more arch-neutral control flow?
>>>>>>>
>>>>>>> e.g.
>>>>>>> #if IS_ENABLED(CONFIG_X86)
>>>>>>> ...
>>>>>>> #else
>>>>>>> ...
>>>>>>> #endif
>>>>>>>
>>>>>>> Would we also prefer this RFC series be merged or would it be preferred to
>>>>>>> create a new series instead?
>>>>>>
>>>>>> for this specific function, that is used in only 2 places I think it's
>>>>>> ok to do:
>>>>>>
>>>>>> 	static inline bool run_as_guest(void)
>>>>>> 	{
>>>>>> 	#if IS_ENABLED(CONFIG_X86)
>>>>>> 		return !hypervisor_is_type(X86_HYPER_NATIVE);
>>>>>> 	#else	
>>>>>> 		/* Not supported yet */
>>>>>> 		return false;	
>>>>>> 	#endif
>>>>>> 	}
>>>>>>
>>>>>> For PCH it doesn't really matter as we don't execute that function
>>>>>> for discrete. For intel_vtd_active() I figure anything other than
>>>>>> x86 would be fine with false here.
>>>>>>
>>>>>> Jani, that this look good to you?
>>>>>
>>>>> It's more important to me to get this out of i915_drv.h, which is not
>>>>> supposed to be a collection of random stuff anymore. I've sent patches
>>>>> to this effect but they've stalled a bit.
>>>>
>>>> do you have a patch moving this particular one? got a link?
>>>
>>> Yeah, but it was basically shot down by Tvrtko [1], and I stalled there.
>>>
>>> I'd just like to get all this cruft out of i915_drv.h. Whenever we have
>>> a file where the name isn't super specific, we seem to have a tendency
>>> of turning it into a dumping ground for random crap. So I'd really like
>>> to move this out of there *before* expanding on it.
>>
>> Sounds like we had agreement on what tweaks to make and I conceded to
>> live for now with the IMO wrongly named intel_vtd_run_as_guest.
>>
>> (I mean I really disagree with file name being trumps, which I think
>> this example illustrates - this is i915 asking whether the kernel is
>> running as guest so intel_vtd_ prefix is just wrong. Intel VT-d is the
>> iommu thingy so it makes no sense when called from PCH detection. But I
>> have no better ideas at the moment. We can call it i915_run_as_guest, to
>> signify function belongs to i915, but then we lose the first parameter
>> names the function rule.)
> 
> I think the "first parameter names the function" rule has backfired in
> gem/gt land, because it's pretty difficult to figure out *where* you'd
> expect to find or place functions.

Hey surely is not that bad. And I am sure if I tried to add some display 
feature that there's a chance I'd manage to misplace something. :))

No scheme is perfect and there are always edge cases, ambiguities and 
always work to cleanup further because it all evolved rather than 
started from scratch. If you know what the function you wrote is about, 
surely you can place it into a file whose name suggests it is the right 
area. If you want the example of GT, there is a nice collection of files 
per functional area.. intel_gt_<suffix>.. interrupts, power management, 
requests, debugfs, etc.

And if you look for functions you did not write, I certainly suggest 
using ctags rather than try opening random files. I think driver is just 
too big for the latter approach.

Regards,

Tvrtko


> BR,
> Jani.
> 
>>
>> But in any case I don't see that I created any blockers in this thread.
>> AFAICS just a respin with intel_vtd_active taking struct device is
>> needed and job done.
>>
>> Regards,
>>
>> Tvrtko
>