linux-kernel - Re: [PATCH v9 4/6] iommu/arm-smmu-v3: Add CS_NONE quirk for CONFIG_TEGRA241

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Message-ID: <ZowqdsN75nb2TD87@Asurada-Nvidia>
Date: Mon, 8 Jul 2024 11:05:42 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Will Deacon <will@...nel.org>
CC: <robin.murphy@....com>, <joro@...tes.org>, <jgg@...dia.com>,
	<thierry.reding@...il.com>, <vdumpa@...dia.com>, <jonathanh@...dia.com>,
	<linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v9 4/6] iommu/arm-smmu-v3: Add CS_NONE quirk for
 CONFIG_TEGRA241_CMDQV

On Mon, Jul 08, 2024 at 12:43:26PM +0100, Will Deacon wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Mon, Jul 08, 2024 at 12:29:28PM +0100, Will Deacon wrote:
> > On Fri, Jul 05, 2024 at 11:10:42AM -0700, Nicolin Chen wrote:
> > > But if you insist on having an smmu option, we still have to take in the
> > > PATCH-3 in this series, enforcing an arm_smmu_cmdq_build_sync_cmd() call
> > > in the IRQ handler too.  So, it would eventually look like [attachment].
> >
> > With my hacks, I think you can just call arm_smmu_cmdq_build_sync_cmd()
> > from the irqhandler and it will work.
> 
> Hmm, actually, that will mean we end up using MSIs for the error case on
> hardware which supports it, which is a strange change in behaviour.

Yes. I highlighted the smae in the commit log of PATCH-3:
   iommu/arm-smmu-v3: Enforce arm_smmu_cmdq_build_sync_cmd

Do you foresee some potential risk of doing that?

> What does your hardware do if it sees SIG_SEV in a CMD_SYNC? Is it just
> a case of failing to generate the event on completion, or does it treat
> it as an invalid opcode?

That would be an invalid opcode.

Thanks
Nicolin