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

[Daniel Vetter]

On Fri, Dec 09, 2016 at 09:47:56PM +0000, Chris Wilson wrote:
> 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);

Well that mutex_lock is fiction too. It's not needed for any of the lists,
and it definitely doesn't protect connector_list. Step-by-step I'd say ...
-Daniel

> 
> 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

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch