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

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Message-ID: <20240702184942.GD5167@willie-the-truck>
Date: Tue, 2 Jul 2024 19:49:42 +0100
From: Will Deacon <will@...nel.org>
To: Nicolin Chen <nicolinc@...dia.com>
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 Tue, Jul 02, 2024 at 11:19:56AM -0700, Nicolin Chen wrote:
> Hi Will,
> 
> On Tue, Jul 02, 2024 at 06:43:07PM +0100, Will Deacon wrote:
> > On Wed, Jun 12, 2024 at 02:45:31PM -0700, Nicolin Chen wrote:
> > > The CMDQV extension in NVIDIA Tegra241 SoC only supports CS_NONE in the
> > > CS field of CMD_SYNC. Add a quirk flag to accommodate that.
> > >
> > > Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> > > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > > ---
> > >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 8 +++++++-
> > >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 3 +++
> > >  2 files changed, 10 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > index c864c634cd23..ba0e24d5ffbf 100644
> > > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > @@ -345,6 +345,11 @@ static void arm_smmu_cmdq_build_sync_cmd(u64 *cmd, struct arm_smmu_device *smmu,
> > >                FIELD_PREP(CMDQ_SYNC_0_MSH, ARM_SMMU_SH_ISH) |
> > >                FIELD_PREP(CMDQ_SYNC_0_MSIATTR, ARM_SMMU_MEMATTR_OIWB);
> > >
> > > +     if (q->quirks & CMDQ_QUIRK_SYNC_CS_NONE_ONLY) {
> > > +             cmd[0] |= FIELD_PREP(CMDQ_SYNC_0_CS, CMDQ_SYNC_0_CS_NONE);
> > > +             return;
> > > +     }
> > > +
> > >       if (!(smmu->options & ARM_SMMU_OPT_MSIPOLL)) {
> > >               cmd[0] |= FIELD_PREP(CMDQ_SYNC_0_CS, CMDQ_SYNC_0_CS_SEV);
> > >               return;
> > > @@ -690,7 +695,8 @@ static int arm_smmu_cmdq_poll_until_sync(struct arm_smmu_device *smmu,
> > >                                        struct arm_smmu_cmdq *cmdq,
> > >                                        struct arm_smmu_ll_queue *llq)
> > >  {
> > > -     if (smmu->options & ARM_SMMU_OPT_MSIPOLL)
> > > +     if (smmu->options & ARM_SMMU_OPT_MSIPOLL &&
> > > +         !(cmdq->q.quirks & CMDQ_QUIRK_SYNC_CS_NONE_ONLY))
> > >               return __arm_smmu_cmdq_poll_until_msi(smmu, cmdq, llq);
> > >
> > >       return __arm_smmu_cmdq_poll_until_consumed(smmu, cmdq, llq);
> > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > > index 180c0b1e0658..01227c0de290 100644
> > > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > > @@ -543,6 +543,9 @@ struct arm_smmu_queue {
> > >
> > >       u32 __iomem                     *prod_reg;
> > >       u32 __iomem                     *cons_reg;
> > > +
> > > +#define CMDQ_QUIRK_SYNC_CS_NONE_ONLY BIT(0)  /* CMD_SYNC CS field supports CS_NONE only */
> > > +     u32                             quirks;
> > 
> > Please can you use the existing smmu->options field instead of adding
> > another place to track quirks? Or do you need this only for some of the
> > queues for a given SMMU device?
> 
> VCMDQs are extension of a regular SMMU (with its own CMDQ). So,
> SMMU CMDQ still supports SIG_IRQ for the CS field, while VCMDQs
> could only support SIG_NONE. In another word, this quirk is not
> per SMMU but per Queue.
> 
> I can highlight this in the commit message, if that would make
> it clear.

I think we could still use smmu->options and have something like
ARM_SMMU_OPT_SECONDARY_CMDQ_CS_NONE_ONLY which could be applied
when the queue is != arm_smmu_get_cmdq(smmu).

Will