linux-kernel - Re: [PATCH v1] drm: add ARM interleaved 64k modifier

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Message-ID: <20260126100545.08a4ffd1@fedora>
Date: Mon, 26 Jan 2026 10:05:45 +0100
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Caterina Shablia <caterina.shablia@...labora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, kernel@...labora.com,
 "Steven Price" <steven.price@....com>, "Liviu Dudau" <liviu.dudau@....com>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] drm: add ARM interleaved 64k modifier

Hello Caterina,

On Fri, 23 Jan 2026 21:23:25 +0000
Caterina Shablia <caterina.shablia@...labora.com> wrote:

> This modifier is intended to be used by panvk to implement sparse
> partially-resident images with better map and unmap performance,
> and no worse access performance, compared to implementing them in
> terms of U-interleaved.
> 
> With this modifier, the arrangement of texel blocks is very similar
> to block U-interleaved. Tiles are laid out linearly. Tiles are
> always 64k bytes in size and are 1:1-sided rectangles when texel
> block is 1 byte or a multiple of 4 bytes, and 2:1-sided otherwise.

It's not all that clear that we're dealing with mega tiles formed with
a set of U-interleaved tiles. Also, the 1:1-sided rectangle sounds
like a complex way to qualify a square.

"
This modifier is a exposing mega tiles of 64 KiB. It's formed of
U-interleaved tiles laid out linearly to cover a square or a rectangle
whose width is twice the height.
"

> Only power of two byte texel blocks can be used with this modifier.
> Within a single tile, texels are arranged according to U-interleaving.
> 
> Unlike block U-interleaved, the layout depends solely on texel block
> size and doesn't change depending on whether the image format is
> compressed or not.

Hm, are you sure of that? I'd assume the inner tile size to still
depend on compressed vs !compressed, meaning the overall layout is also
dependent on the compressed vs !compressed property.

> 
> The hardware features corresponding to this modifier are available
> starting with v10 (second gen Valhall.)
> 
> The corresponding panvk MR can be found at:
> https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38986
> 
> Signed-off-by: Caterina Shablia <caterina.shablia@...labora.com>
> ---
>  include/uapi/drm/drm_fourcc.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
> index e527b24bd824..0da2c880e08c 100644
> --- a/include/uapi/drm/drm_fourcc.h
> +++ b/include/uapi/drm/drm_fourcc.h
> @@ -1422,6 +1422,16 @@ drm_fourcc_canonicalize_nvidia_format_mod(__u64 modifier)
>  #define DRM_FORMAT_MOD_ARM_16X16_BLOCK_U_INTERLEAVED \
>  	DRM_FORMAT_MOD_ARM_CODE(DRM_FORMAT_MOD_ARM_TYPE_MISC, 1ULL)
>  
> +/*
> + * ARM 64k interleaved modifier
> + *
> + * This is used by ARM Mali v10+ GPUs. It's basically the same as 16x16 block
> + * U-interleaved, but within 64k-byte 1:1 or 2:1 -sided tiles.

Again, it's not clear from this description that this modifier is
exposing "mega" tiles formed with a set of U-interleaved tiles spanning
a 64KiB section. The way I read this is that it's U-interleaved, but
over a bigger region, like 256x256 U-interleaved.

Regards,

Boris

> Tiles themselves
> + * are laid out linearly.
> + */
> +#define DRM_FORMAT_MOD_ARM_INTERLEAVED_64K \
> +	DRM_FORMAT_MOD_ARM_CODE(DRM_FORMAT_MOD_ARM_TYPE_MISC, 2ULL)
> +
>  /*
>   * Allwinner tiled modifier
>   *
> 
> base-commit: f08f665f8cda9520d98ee24545d306a92f386616