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References: <20220214203132.4722-1-alyssa.rosenzweig@collabora.com>
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From:   Rob Herring <robh@kernel.org>
Date:   Tue, 15 Feb 2022 15:53:07 -0600
Message-ID: <CAL_JsqKdb0_N252hR=iv3Lpi6T9+iCRBwzBQhS7UQGFNhM5k=A@mail.gmail.com>
Subject: Re: [PATCH] drm/panfrost: Dynamically allocate pm_domains
To:     Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Cc:     dri-devel <dri-devel@lists.freedesktop.org>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Steven Price <steven.price@arm.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
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On Mon, Feb 14, 2022 at 2:31 PM Alyssa Rosenzweig
<alyssa.rosenzweig@collabora.com> wrote:
>
> MT8192 requires 5 power domains. Rather than bump MAX_PM_DOMAINS and
> waste memory on every supported Panfrost chip, instead dynamically
> allocate pm_domain_devs and pm_domain_links. This adds some flexibility;
> it seems inevitable a new MediaTek device will require more than 5
> domains.
>
> On non-MediaTek devices, this saves a small amount of memory.

How much? You measured it?

It's not that simple. kmalloc has finite allocation sizes (see
/proc/slabinfo). So unless panfrost_device shrinks or grows to the
next smaller or larger size, the memory used doesn't change. And each
devm_kmalloc adds its own overhead as well.

I'd do the oneliner changing it to 5 and be done with it. That being
said, we have plenty of examples of doing this both ways, so whatever
makes people happy.

Rob