[PATCH 10/10] drm/imx: ipuv3-plane: use drm_plane_helper_check_state, clipped coordinates

[Ying Liu]

On Fri, Oct 21, 2016 at 4:18 PM, Philipp Zabel <p.zabel at pengutronix.de> wrote:
> Am Freitag, den 21.10.2016, 13:45 +0800 schrieb Ying Liu:
>> On Thu, Oct 20, 2016 at 9:29 PM, Philipp Zabel <p.zabel at pengutronix.de> wrote:
>> > Am Donnerstag, den 20.10.2016, 16:51 +0800 schrieb Ying Liu:
>> >> >> Does the clip thing potentially change the user's request by force?
>> >> >> For example, the user request an unreasonable big resolution.
>> >> >
>> >> > The user is allowed to ask for destination coordinates extending outside
>> >> > the crtc dimensions. This will chop off the parts that aren't visible,
>> >> > and it will chop off the corresponding areas of the source as well.
>> >>
>> >> How about returning -EINVAL in this case which stands for
>> >> an atomic check failure?
>> >
>> > Say the user requests to display a 640x480+0,0 source framebuffer at
>> > destination offset -320,0 on a 320x240 screen, unscaled. The expectation
>> > would be to see the upper right quarter of the framebuffer on the
>> > screen, at least if the hardware was actually able to position overlays
>> > partially offscreen.
>> > If we can also fulfill that expectation by clipping the source rectangle
>> > to 320,240+320,0 and changing the destination rectangle to 320x240+0,0,
>> > why should -EINVAL be returned?
>>
>> Well, IIUC, there are two kinds of clipping.
>> 1) Clipping a rectangle from a fb according to src_x/y and src_w/h.
>> 2) Clipping done by drm_plane_helper_check_state(), which potentially
>>     changes src/dst->x1/2 and src/dst->y1/2(in other words, src_x/y,
>>     src_w/h and crtc_x/y/w/h, though not directly).
>>
>> 1) is fine, no problem.
>> I doubt 2) is wrong as the users' original request could be changed.
>> That's why I mentioned returning -EINVAL.
>>
>> Moreover, before and after applying the patch, I think the
>> ->atomic_check behavior consistency is broken. For example,
>> negative crtc_x or crtc_y for overlay are changed from unacceptable
>> to potentially acceptable just because 2) may change their equivalent
>> dst_>x/y1.
>
> I fail to see what's wrong with 2) as long as we can keep the observable
> behaviour exactly the same as if the user request was unchanged.

It seems the behavior could change - negative crtc_x or crtc_y for
overlay make ->atomic_check return -EINVAL before(overlay hw state
machine has nothing changed), and potentially successful after(overlay
hw state machine changes).

Regards,
Liu Ying

>
> regards
> Philipp
>