Re: [PATCH 0/3] SM8450 IPA support

[Esteban Urrutia]

On 7/8/26 3:49 PM, Alex Elder wrote:
> This was interesting to see.  It's something I should probably
> document better.  Most everything maps to the downstream code,
> but it's not always completely obvious how, because the upstream
> driver has evolved substantially.

On a personal note, I'm surprised to see someone not from Qualcomm
maintaining this driver. It must be hard, so kudos.

> This means that the SRAM size (ipa_mem_data->smem_size) should
> possibly be defined in devicetree (as the IMEM address and size
> now are).
> 
> The SMEM region is used for "IPA filter tables", and access to
> it is shared between the AP and the modem.  Unlike the other
> (host) memory regions, the size used is *not* included in the
> ipa_init_modem_driver_req message that communicates from the
> AP to the modem where the regions are, and their sizes.
> 
> So it's possible that the size used must actually match what
> is expected by both the AP and modem.  If that is the case,
> using the smaller size might have problems on whichever
> platform (SM8450?) expects the larger one.
> 
> So I'm not sure whether using the smaller size for both
> platforms is OK; someone from Qualcomm might be able to
> answer that question.

I actually went ahead and reviewed downstream device trees I found on
GitHub (1) which contain both SM8450 and SM8475 device trees looking for
the qcom,ipa-q6-smem-size property, which would correspond to the SRAM
size, and to my surprise, this was set to 0x9000 for both SoCs.
Most likely the commit I got the SRAM information from (2) never made it
to production devices.

With this clarified, I think it should be okay to keep things defined as
they currently are.

> I'll try to explain those things separately.
Regarding this, I have a question: where would this be published?

Thanks for taking the time to properly review my changes.
I'll address the review when I can.

(1) https://github.com/sm8450-mainline/fdt
(2) https://github.com/LineageOS/android_kernel_qcom_sm8450-devicetrees/commit/477aab9e7479ff553c7a162ae74029170a2e8291.patch

Regards,
Esteban