Re: [PATCH 0/3] SM8450 IPA support

[Konrad Dybcio]

On 7/8/26 10:45 PM, Esteban Urrutia wrote:
> 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.

OK you meant the qcom,ipa-q6-smem-size property. I can't find what
it corresponds to, the name of the associated IOMMU stream
unfortunately doesn't hint at anything useful either..

Konrad