linux-kernel - Re: [PATCH 1/1] ARM: dts: imx6qdl: Add reserved memory area for CMA memory

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Message-ID: <3313261.aeNJFYEL58@steina-w>
Date: Wed, 28 Aug 2024 08:12:20 +0200
From: Alexander Stein <alexander.stein@...tq-group.com>
To: Fabio Estevam <festevam@...il.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>, linux@...tq-group.com, devicetree@...r.kernel.org, imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ARM: dts: imx6qdl: Add reserved memory area for CMA memory

Am Dienstag, 27. August 2024, 16:32:10 CEST schrieb Fabio Estevam:
> Hi Alexander,
> 
> On Tue, Aug 27, 2024 at 11:25 AM Alexander Stein
> <alexander.stein@...tq-group.com> wrote:
> >
> > Default CMA size is too small for HDMI output and VPU usage. Increase the
> > default size by providing a CMA memory area.
> ....
> > +               linux,cma {
> > +                       compatible = "shared-dma-pool";
> > +                       reusable;
> > +                       size = <0x14000000>;
> 
> Just curious: how did you calculate that this is a suitable CMA memory
> area size?

Just after startup and a simple weston running on a 1080 HDMI output I habe
this CMA status:
> # grep Cma /proc/meminfo
> CmaTotal:         327680 kB
> CmaFree:          137764 kB

AFAIK also DMA setup is using CMA memory.

When playing (and decoding) bbb_sunflower_1080p_30fps_normal.mp4 free CMA memory
shrinks down to ~60MiB
> # grep Cma /proc/meminfo
> CmaTotal:         327680 kB
> CmaFree:           63144 kB

So, 260MiB should be enough (but just barely). But to give some spare memory
it has been increased to 320MiB.

Best regards,
Alexander
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