[PATCH v2 1/7] drm/xe: Introduce const cast helper

[Lucas De Marchi]

On Fri, Jul 19, 2024 at 06:55:43PM GMT, Michal Wajdeczko wrote:
>
>
>On 19.07.2024 18:32, Lucas De Marchi wrote:
>> On Wed, Jul 17, 2024 at 09:51:49PM GMT, Michal Wajdeczko wrote:
>>> Typically we want to preserve pointer constness when converting
>>> from one xe pointer to another, but in some rare cases, like kunit
>>> parameter conversions, we might want to discard this constness.
>>> Add a helper that we will use to clearly indicate our intention.
>>>
>>> Signed-off-by: Michal Wajdeczko <michal.wajdeczko at intel.com>
>>> ---
>>> drivers/gpu/drm/xe/xe_device.h | 5 +++++
>>> 1 file changed, 5 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/xe/xe_device.h
>>> b/drivers/gpu/drm/xe/xe_device.h
>>> index 0a2a3e7fd402..c2b1f9f066bd 100644
>>> --- a/drivers/gpu/drm/xe/xe_device.h
>>> +++ b/drivers/gpu/drm/xe/xe_device.h
>>> @@ -20,6 +20,11 @@ static inline struct xe_device
>>> *pdev_to_xe_device(struct pci_dev *pdev)
>>>     return pci_get_drvdata(pdev);
>>> }
>>>
>>> +static inline struct xe_device *xe_device_const_cast(const struct
>>> xe_device *xe)
>>> +{
>>> +    return pdev_to_xe_device(to_pci_dev(xe->drm.dev));
>>
>> why are you going through pdev_to_xe_device() rather than doing what the
>> function name says and just remove the const?
>
>IIRC this was my initial way how to get rid of the const without doing a
>forced cast and it was before I decided to introduce a helper for it and
>before this helper was named this way ;)
>
>and while explicit cast is more direct (and I can still do that way in
>next rev if preferred), then it will be just pure C language concept,
>while the potential advantage of doing that through pdev_to_xe_device()
>is that it shows that this non-const xe pointer could be still obtained
>indirectly, so it should be safe to do so

it just relies on to_pci_dev() dropping the constness by using pointer
arithmetic to get the outer object. It's as safe as doing the most
obvious thing for this particular case: a cast.

Lucas De Marchi

>
>>
>> Lucas De Marchi
>>
>>> +}
>>> +
>>> static inline struct xe_device *ttm_to_xe_device(struct ttm_device *ttm)
>>> {
>>>     return container_of(ttm, struct xe_device, ttm);
>>> -- 
>>> 2.43.0
>>>