Message-ID: <566A6C97.4020207@rock-chips.com>
Date:	Fri, 11 Dec 2015 14:26:31 +0800
From:	Mark yao <mark.yao@...k-chips.com>
To:	Daniel Stone <daniel@...ishbar.org>
CC:	David Airlie <airlied@...ux.ie>, Heiko Stuebner <heiko@...ech.de>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-rockchip <linux-rockchip@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tomasz Figa <tfiga@...omium.org>
Subject: Re: [RFC PATCH 3/9] drm/rockchip: Convert to support atomic API

On 2015年12月02日 22:18, Daniel Stone wrote:
> Hi Mark,
> Thanks for getting back to this.
>
> On 1 December 2015 at 09:31, Mark yao <mark.yao@...k-chips.com> wrote:
>> On 2015年12月01日 16:18, Daniel Stone wrote:
>>> On 1 December 2015 at 03:26, Mark Yao<mark.yao@...k-chips.com>  wrote:
>>>>> +       for_each_crtc_in_state(state, crtc, crtc_state, i) {
>>>>> +               if (!crtc->state->active)
>>>>> +                       continue;
>>>>> +
>>>>> +               rockchip_crtc_wait_for_update(crtc);
>>>>> +       }
>>> I'd be much more comfortable if this passed in an explicit pointer to
>>> state, or an address to wait for, rather than have wait_for_complete
>>> dig out state with no locking. The latter is potentially racy for
>>> async operations.
>>>
>> Hi Daniel
>>     "if this passed in an explicit pointer to state, or an address to wait
>> for", I don't understand, can you point how it work?
> Ah, OK. I mean that rockchip_crtc_wait_for_update takes a drm_crtc
> pointer, and establishes the state from that (e.g.
> crtc->primary->state). This can easily lead to confusion in async
> contexts, as the states attached to a drm_crtc and a drm_plane can
> change here while you wait for it.
>
> It would be better if the call was:
>
> for_each_plane_in_state(state, plane, plane_state, i) {
>      if (plane->type == DRM_PLANE_TYPE_PRIMARY)
>          rockchip_crtc_wait_for_update(plane_state->crtc, plane_state);
> }
>
> This way it is very clear, and there is no confusion as to which
> request we are waiting to complete.
>
> In general, using crtc->state or plane->state is a very bad idea,
> _except_ in the atomic_check function where you are calculating
> changes (e.g. if (plane_state->fb->pitches[0] !=
> plane->state->fb->pitches[0]) rockchip_plane_state->pitch_changed =
> true). After atomic_check, you should always pass around pointers to
> the plane state explicitly, and avoid using the pointers from drm_crtc
> and drm_plane.
>
> Does that help?

Hi Daniel

Sorry, I don't actually understand why crtc->state or plane->state is no 
recommended
except atomic_check, on atomic_update, we need use plane->state, is that 
a problem?

I guess that, drm_atomic_helper_swap_state would race with async operations,
so use crtc->state on async stack is not safe. is it correct?

I think we can make asynchronous commit serialize as tegra drm done to 
avoid this problem:


   86         /* serialize outstanding asynchronous commits */
   87 mutex_lock(&tegra->commit.lock);
   88 flush_work(&tegra->commit.work);
89
   90 /*
   91          * This is the point of no return - everything below never 
fails except
   92          * when the hw goes bonghits. Which means we can commit 
the new state on
   93          * the software side now.
   94 */
95
   96         drm_atomic_helper_swap_state(drm, state);
97
   98         if (async)
   99                 tegra_atomic_schedule(tegra, state);
  100 else
  101                 tegra_atomic_complete(tegra, state);
  102
  103         mutex_unlock(&tegra->commit.lock);


>
>>>>           if (is_yuv) {
>>>>                   /*
>>>>                    * Src.x1 can be odd when do clip, but yuv plane start
>>>> point
>>>>                    * need align with 2 pixel.
>>>>                    */
>>>> -               val = (src.x1 >> 16) % 2;
>>>> -               src.x1 += val << 16;
>>>> -               src.x2 += val << 16;
>>>> +               uint32_t temp = (src->x1 >> 16) % 2;
>>>> +
>>>> +               src->x1 += temp << 16;
>>>> +               src->x2 += temp << 16;
>>>>           }
>>> I know this isn't new, but moving the plane around is bad. If the user
>>> gives you a pixel boundary that you can't actually use, please reject
>>> the configuration rather than silently trying to fix it up.
>> the origin src.x1 would align with 2 pixel, but when we move the dest
>> window, and do clip by output, the src.x1 may be clipped to odd.
>> regect this configuration may let user confuse, sometimes good, sometimes
>> bad.
> For me, it is more confusing when the display shows something
> different to what I have requested. In some media usecases, doing this
> is a showstopper and will result in products failing acceptance
> testing. Userspace can make a policy decision to try different
> alignments to get _something_ to show (even if it's not what was
> explicitly requested), but doing this in the kernel is inappropriate:
> please just reject it, and have userspace fall back to another
> composition method (e.g. GL) in these cases.
>
>>>> -static void vop_plane_destroy(struct drm_plane *plane)
>>>> +static void vop_atomic_plane_destroy_state(struct drm_plane *plane,
>>>> +                                          struct drm_plane_state *state)
>>>>    {
>>>> -       vop_disable_plane(plane);
>>>> -       drm_plane_cleanup(plane);
>>>> +       struct vop_plane_state *vop_state = to_vop_plane_state(state);
>>>> +
>>>> +       if (state->fb)
>>>> +               drm_framebuffer_unreference(state->fb);
>>>> +
>>>> +       kfree(vop_state);
>>>>    }
>>> You can replace this hook with drm_atomic_helper_plane_destroy_state.
>>
>> Hmm, only can hook with __drm_atomic_helper_plane_destroy_state.
> Ah yes, you're right. But still, using that would be better than duplicating it.
>
>>      Can you share your Weston environment to me, I'm interesting to test drm
>> rockchip on weston.
> Of course. You can download Weston from http://wayland.freedesktop.org
> - the most interesting dependencies are libevdev, libinput, and
> wayland itself. If you are building newer Weston from git, you'll need
> the wayland-protocols repository as well, from
> anongit.freedesktop.org/git/wayland/wayland-protocols/. Please let me
> know privately if you need some more help with building these, but
> they should be quite straightforward.
>
> Cheers,
> Daniel
>
>
>


-- 
Ｍark Yao


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