Re: [PATCH v7 02/12] firmware: qcom: scm: enable the TZ mem allocator

Bartosz Golaszewski
2024-02-27T08:25:02Z

On Mon, Feb 26, 2024 at 11:30 AM Kuldeep Singh
<quic_kuldsing@quicinc.com> wrote:
>
> > > > As we're not moving from the callers freely allocating what they need,
> > > > to a fixed sized pool of 256kb. Please document why 256kb was choosen,
> > > > so that we have something to fall back on when someone runs out of this
> > > > space, or wonders "why not 128kb?".
> > > >
> > >
> > > If you worry about these pools being taken out of the total memory and
> > > prefer to have a way to avoid it, I was thinking about another
> > > build-time mode for the allocator - one where there's no pool but it
> > > just allocates chunks using dma_alloc_coherent() like before and pool
> > > size is ignored. Does it sound good?
> > >
> >
> > Or we could even have an argument for the initial size of the pool and
> > then once it's exhausted, we'd add a new chunk (maybe twice the size?)
> > and so on.
>
> Hi Bartosz,
>
> Thanks for shmbridge patch series. Few questions.
>
> 1. With current design of every client maintaining it's own pool,
> For any target, we might end up occupying lot more space by
> different clients than we actually need.
>

Technically there are only up to two, three in the future with scminvoke.

> 2. Also, there's no option to configure pool size for each client at
> runtime level and a fixed 256K value is chosen for qcom_scm/qseecom.

You mean via a module parameter?

> Pool size will be same for each target and thus making it less
> scalabale if there's adjustment needed at target specific level.
> Ex: For a low DDR memory target, pool size should scale down accordingly
> as 256K will become a big ask but there's no way to choose specific pool
> size for just one target.

Do we really have any low-DDR platforms that would be affected by this
change? Even for db401c the 256K is a tiny fraction of the total
memory.

> 2.1 One way to do configure custom pool size value is to add new
> property in qcom_scm/qseecom or client DT node and then create
> pool of size with this provided value. Though there are ways to
> tackle this, but still clients specifying it's own pool size
> will always fetch more CMA region than what is actually needed.
>
> Can you please share your ideas as well for upcoming version.
>

I will propose a new solution with several configuration options for
pools. Including scaling the pool size as needed. I hope to send it
this week.

Bart

> Regards
> Kuldeep