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Date:   Mon, 18 Oct 2021 10:53:33 +0300
From:   Pekka Paalanen <ppaalanen@gmail.com>
To:     Igor Matheus Andrade Torrente <igormtorrente@gmail.com>
Cc:     rodrigosiqueiramelo@gmail.com, melissa.srw@gmail.com,
        hamohammed.sa@gmail.com, daniel@ffwll.ch, airlied@linux.ie,
        contact@emersion.fr, leandro.ribeiro@collabora.com,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        lkcamp@lists.libreplanetbr.org
Subject: Re: [PATCH 0/6] Refactor the vkms to accept new formats
Message-ID: <20211018105333.5f1bf9fe@eldfell>
In-Reply-To: <20211005201637.58563-1-igormtorrente@gmail.com>
References: <20211005201637.58563-1-igormtorrente@gmail.com>
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On Tue,  5 Oct 2021 17:16:31 -0300
Igor Matheus Andrade Torrente <igormtorrente@gmail.com> wrote:

> XRGB to ARGB behavior
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> During the development, I decided to always fill the alpha channel of
> the output pixel whenever the conversion from a format without an alpha
> channel to ARGB16161616 is necessary. Therefore, I ignore the value
> received from the XRGB and overwrite the value with 0xFFFF.
>=20
> My question is, is this behavior acceptable?

Hi,

that is the expected behaviour. X channel values must never affect
anything on screen, hence they must never affect other channels'
values. You are free to completely ignore X channel values, and if your
output buffer has X channel, then you are free to write (or not write,
unless for security reasons) whatever into it.


Thanks,
pq

>=20
> [1] https://lists.freedesktop.org/archives/igt-dev/2021-October/036125.ht=
ml
>=20
> Igor Matheus Andrade Torrente (6):
>   drm: vkms: Replace the deprecated drm_mode_config_init
>   drm: vkms: Alloc the compose frame using vzalloc
>   drm: vkms: Replace hardcoded value of `vkms_composer.map` to
>     DRM_FORMAT_MAX_PLANES
>   drm: vkms: Add fb information to `vkms_writeback_job`
>   drm: vkms: Prepare `vkms_wb_encoder_atomic_check` to accept multiple
>     formats
>   drm: vkms: Refactor the plane composer to accept new formats
>=20
>  drivers/gpu/drm/vkms/vkms_composer.c  | 275 ++++++++++++++------------
>  drivers/gpu/drm/vkms/vkms_drv.c       |   5 +-
>  drivers/gpu/drm/vkms/vkms_drv.h       |  12 +-
>  drivers/gpu/drm/vkms/vkms_formats.h   | 125 ++++++++++++
>  drivers/gpu/drm/vkms/vkms_writeback.c |  27 ++-
>  5 files changed, 304 insertions(+), 140 deletions(-)
>  create mode 100644 drivers/gpu/drm/vkms/vkms_formats.h
>=20


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