Re: [PATCH 2/2] drm/lima: driver for ARM Mali4xx GPUs

[Eric Anholt <eric@anholt.net>]

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Qiang Yu <yuq825@gmail.com> writes:

> On Thu, Feb 7, 2019 at 3:17 AM Eric Anholt <eric@anholt.net> wrote:
>>
>> Qiang Yu <yuq825@gmail.com> writes:
>> > +int lima_gem_wait(struct drm_file *file, u32 handle, u32 op, u64 timeout_ns)
>> > +{
>> > +     bool write = op & LIMA_GEM_WAIT_WRITE;
>> > +     struct drm_gem_object *obj;
>> > +     struct lima_bo *bo;
>> > +     signed long ret;
>> > +     unsigned long timeout;
>> > +
>> > +     obj = drm_gem_object_lookup(file, handle);
>> > +     if (!obj)
>> > +             return -ENOENT;
>> > +
>> > +     bo = to_lima_bo(obj);
>> > +
>> > +     timeout = timeout_ns ? lima_timeout_to_jiffies(timeout_ns) : 0;
>> > +
>> > +     ret = lima_bo_reserve(bo, true);
>> > +     if (ret)
>> > +             goto out;
>> > +
>> > +     /* must use long for result check because in 64bit arch int
>> > +      * will overflow if timeout is too large and get <0 result
>> > +      */
>> > +     ret = reservation_object_wait_timeout_rcu(bo->tbo.resv, write, true, timeout);
>> > +     if (ret == 0)
>> > +             ret = timeout ? -ETIMEDOUT : -EBUSY;
>> > +     else if (ret > 0)
>> > +             ret = 0;
>> > +
>> > +     lima_bo_unreserve(bo);
>> > +out:
>> > +     drm_gem_object_put_unlocked(obj);
>> > +     return ret;
>> > +}
>>
>> From Documentation/botching-up-ioctls.txt:
>>
>>  * For timeouts, use absolute times. If you're a good fellow and made your
>>    ioctl restartable relative timeouts tend to be too coarse and can
>>    indefinitely extend your wait time due to rounding on each restart.
>>    Especially if your reference clock is something really slow like the display
>>    frame counter. With a spec lawyer hat on this isn't a bug since timeouts can
>>    always be extended - but users will surely hate you if their neat animations
>>    starts to stutter due to this.
>>
>> (I made v3d's timeouts relative, but decrement the timeout value the
>> user passed by how much I waited so that the timeout probably gets
>> reduced after a restartable signal.  I should have done absolute.)
> timeout_ns in lima is already an absolute one which will be converted to
> relative one in lima_timeout_to_jiffies, is this what you want or I miss
> understand?

Yeah, not sure how I missed the lima function, wich is clearly doing
absolute.  Sorry!

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