linux-kernel - Re: [PATCH v4 07/10] PCI/IDE: Add IDE establishment helpers

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Message-ID: <yq5azfbjq2nf.fsf@kernel.org>
Date: Thu, 28 Aug 2025 13:49:32 +0530
From: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
To: Arto Merilainen <amerilainen@...dia.com>, dan.j.williams@...el.com
Cc: linux-kernel@...r.kernel.org, bhelgaas@...gle.com, aik@....com,
	lukas@...ner.de, Samuel Ortiz <sameo@...osinc.com>,
	Yilun Xu <yilun.xu@...ux.intel.com>, linux-pci@...r.kernel.org,
	linux-coco@...ts.linux.dev
Subject: Re: [PATCH v4 07/10] PCI/IDE: Add IDE establishment helpers

Arto Merilainen <amerilainen@...dia.com> writes:

> On 8.8.2025 20.26, dan.j.williams@...el.com wrote:
>> Arto Merilainen wrote:
>>> The first revision of this patch had address association register
>>> programming but it has since been removed. Could you comment if there is
>>> a reason for this change?
>> 
>> We chatted about it around this point in the original review thread [1].
>> tl;dr SEV-TIO and TDX Connect did not see a strict need for it. However,
>> the expectation was always to circle back and revive it if it turned out
>> later to be required.
>
> Thank you for the reference. I suppose it is ok to rely on the default 
> streams on the first iteration, and add a follow-up patch in the ARM CCA 
> device assignment support series in case it is the only architecture 
> that depends on them.
>
>> 
>>> Some background: This might be problematic for ARM CCA. I recall seeing
>>> a comment stating that the address association register programming can
>>> be skipped on some architectures (e.g., apparently AMD uses a separate
>>> table that contains the StreamID) but on ARM CCA the StreamID
>>> association AFAIK happens through these registers.
>> 
>> Can you confirm and perhaps work with Aneesh to propose an incremental
>> patch to add that support back? It might be something that we let the
>> low level TSM driver control. Like an additional address association
>> object that can be attached to 'struct pci_ide' by the low level TSM
>> driver.
>
> Aneesh, could you perhaps extend the IDE driver by adding the RP address 
> association register programming in the next revision of the DA support 
> series?
>

Sure, I can add that change as part of next update. 

>
> I think the EP side programming won't be relevant until we get to the 
> P2P use-cases.
>
>> 
>> The messy part is sparse device MMIO layout vs limited association
>> blocks and this is where SEV-TIO and TDX Connect have other mechanisms
>> to do that stream-id association.
>
> Despite the potential sparsity, I think there needs to be only three 
> address association register blocks per SEL_IDE block: The routing is 
> based on the type-1 configuration space header which defines only three 
> ranges (32bit BAR, 64bit BAR, IO). When enabling IDE between an RP and 
> an EP, the SEL_IDE address association registers in the RP can be 
> programmed with the same ranges used in the type-1 header in the switch 
> upstream from the EP.
>
> That said, if the RP implements less than three address association 
> registers per SEL_SID, this scheme won't work.
>
> (I vaguely recall that the PCIe spec might forbid IORd/IOWr TLPs when 
> selective IDE streams are used so the limit might in fact be two instead 
> three...)
>
> - R2