[PATCH 5/7] drm: Don't compute obj counts expensively in get_resources

[Chris Wilson]

On Fri, Dec 09, 2016 at 03:19:42PM +0100, Daniel Vetter wrote:
> Looping when we keep track of this is silly. Only thing we have to
> be careful is with sampling the connector count. To avoid inconsisten
> results due to gcc re-computing this, use READ_ONCE.

Later on in the function we take the mutex that should prevent the
values from changing.

If each block was like

mutex_lock(&mode_config->lockc);

count = dev->mode_config.num_crtc;
if (card_res->count_crtcs >= count) {
        u32 __user id = u64_to_user_ptr(card_res->crtc_id_ptr);
        unsigned int copied = 0;

        drm_for_each_crtc(crtc, dev) {
                if (copied >= count)
                        break;

                if (put_user(crtc->base.id, id + copied)) {
                        ret = -EFAULT;
                        goto out;
                }

                copied++;
        }

        count = copied;
}
card_res->count_crtcs = count;

...

mutex_unlock(&mode_config->lockc);

it would look a bit neater.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre