linux-kernel - Re: [PATCH 2/3] firmware: qcom: scm: Add function to set the maximum IOMMU pool size

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Message-ID: <c206a619-a40c-8c2b-8dfe-484f2b0eba92@linaro.org>
Date:   Fri, 10 Dec 2021 15:44:58 -0600
From:   Alex Elder <elder@...aro.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        phone-devel@...r.kernel.org, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        ~postmarketos/upstreaming@...ts.sr.ht,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Pavel Dubrova <pashadubrova@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Arnd Bergmann <arnd@...db.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Elliot Berman <eberman@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] firmware: qcom: scm: Add function to set the maximum
 IOMMU pool size

On 12/10/21 10:28 AM, AngeloGioacchino Del Regno wrote:
> Il 09/12/21 00:44, Marijn Suijten ha scritto:
>> On 2021-12-08 07:30:28, Alex Elder wrote:
>>> On 12/8/21 2:34 AM, Marijn Suijten wrote:
>>>> From: AngeloGioacchino Del Regno 
>>>> <angelogioacchino.delregno@...ainline.org>
>>>>
>>>> This is not necessary for basic functionality of the IOMMU, but
>>>> it's an optimization that tells to the TZ what's the maximum
>>>> mappable size for the secure IOMMUs, so that it can optimize
>>>> the data structures in the TZ itself.
>>>
>>> Are there no users of this function?    -Alex
>>
>> I should have probably mentioned in the cover letter that this function
>> and the one introduced in patch 3/3 are going to be used in upcoming
>> patches for IOMMUs found in msm8976, msm8974 and related SoCs (with the
>> side-note that I don't see this particular set_cp_pool_size used in the
>> branch that this was submitted from, but it's most likely used elsewhere
>> or planned ahead to be used in the near future - I expect Angelo to be
>> able to comment on that more accurately).
>>
> 
> This function is used in the secured iommu pagetable setup, but not for
> all of the "SCM feature versions" (only for version >= 1.1.1, downstream
> reads it with a call to scm_feat_version()).
> 
> It's not strictly necessary for functionality, hence why Marijn isn't
> seeing any call to this in the branch that he was browsing: the spirit here
> is to first introduce code that does a minimal (but, of course, working)
> setup of the IOMMUs found in MSM8956/76 (which can be adapted with very
> minimal changes to other SoCs), and *only then* to add these performance
> enhancements to the mix.
> 
> ...and this is why this commit is here :))
> 
> By the way, if my memory isn't failing me, that SCM call should be usable
> on all AArch64 SoCs (so, 8956, 8994 and the rest).

Thanks for your responses.  I don't actually know what
you use as downstream for this.  If I did, I might
compare what I see there to what you do and confirm
it does the same thing...

So I'm not offering any review on this or patch 3.
But I'm glad to know the users of these functions
will be coming soon.

					-Alex