linux-kernel - Re: [PATCH v2 3/5] drm/rockchip: vop: support plane scale

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Message-ID: <CAAFQd5AM1-w8ynyn_Usr8OitdXSUcU85scvcYCTEZebzLqLn0w@mail.gmail.com>
Date:	Fri, 3 Jul 2015 23:37:09 +0900
From:	Tomasz Figa <tfiga@...omium.org>
To:	Mark yao <mark.yao@...k-chips.com>
Cc:	dri-devel <dri-devel@...ts.freedesktop.org>,
	David Airlie <airlied@...ux.ie>,
	Heiko Stuebner <heiko@...ech.de>,
	Daniel Kurtz <djkurtz@...omium.org>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Daniel Vetter <daniel@...ll.ch>,
	Rob Clark <robdclark@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	sandy.huang@...k-chips.com, dkm@...k-chips.com, zwl@...k-chips.com,
	xw@...k-chips.com
Subject: Re: [PATCH v2 3/5] drm/rockchip: vop: support plane scale

On Fri, Jul 3, 2015 at 7:22 PM, Mark yao <mark.yao@...k-chips.com> wrote:
> On 2015年07月03日 17:58, Tomasz Figa wrote:
>>>>
>>>> >>Aren't the scl_modes for CbCr planes always the same as for Y plane?
>>>
>>> >
>>> >
>>> >No, such as src(1920 x 1080) -> dst(1280x800), yuv format is NV12.
>>> >so Y plane horizontal and vertical is scale down.
>>> >
>>> >but src_w = 1920 / 2 = 960 < 1280
>>> >       src_h = 1080 / 2 = 540 < 800.
>>> >
>>> >So Cbcr horizontal and vertical is scale up.
>>
>> Sorry, I don't follow.
>>
>> If we scale down Y plane in NV12 from 1920x1080 to 1280x800, then
>> original CbCr plane will be 960x540 and destination CbCr plane will be
>> 640x400 (because CbCr plane of NV12 is subsampled 2x2, which is half
>> the width and half the height of Y plane), so both planes are being
>> scaled down.
>>
> destination CbCr plane is 1280x800, destination can't be subsample.

Ah, I see, so internally it's always scalling to destination plane
size. This means that calculation for both Y and CbCr must be done
indeed, but even then you could use helper functions for that, since
they differ only in parameters.

Best regards,
Tomasz
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